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FRUITS.remove("apple"); </pre></td></tr></table></figure>将抛出<code>java.lang.UnsupportedOperationException</code>异常：<a id="more"></a> <img src="img/febsvue/QQ截图20190422144849.png" alt="QQ截图20190422144849.png"><h3 id="创建不可变集合"><a href="#创建不可变集合" class="headerlink" title="创建不可变集合"></a>创建不可变集合</h3>of<figure class="highlight java"><table><tr><td class="gutter"><pre>1 2 </pre></td><td class="code"><pre>ImmutableList<String> immutableList = ImmutableList.of("a", "b", "c"); ImmutableMap<Integer, String> immutableMap = ImmutableMap.of(1, "v1", 2, "v2", 3, "v3") </pre></td></tr></table></figure>copyOf<figure class="highlight java"><table><tr><td class="gutter"><pre>1 2 </pre></td><td class="code"><pre>Map<String, String> map = Maps.newHashMap(); ImmutableMap<String, String> immutableMap = ImmutableMap.copyOf(map); </pre></td></tr></table></figure>builder<figure class="highlight java"><table><tr><td class="gutter"><pre>1 2 3 4 5 6 7 8 9 10 </pre></td><td class="code"><pre>Map<String, String> map = Maps.newHashMap(); ImmutableMap<String, String> immutableMap = ImmutableMap.<String, String>builder() .putAll(map) .put("k1", "v1") .build(); List<String> list = Lists.newArrayList(); ImmutableList<String> immutableList = ImmutableList.<String>builder() .addAll(list) .build(); </pre></td></tr></table></figure>除此之外，我们也可以从Java 8 Stream中创建不可变集合：<figure class="highlight java"><table><tr><td class="gutter"><pre>1 2 3 4 5 6 7 8 </pre></td><td class="code"><pre>import static java.util.stream.Collectors.*; ... List<String> list = Arrays.asList("a", "b", "c"); List<String> immutableList = list.stream() .collect(collectingAndThen(toList(), ImmutableList::copyOf)); System.out.println(immutableList.getClass()); // class com.google.common.collect.RegularImmutableList </pre></td></tr></table></figure>上面的例子我们也可以使用Guava提供的收集器：<figure class="highlight java"><table><tr><td class="gutter"><pre>1 2 3 4 5 </pre></td><td class="code"><pre>List<String> list = Arrays.asList("a", "b", "c"); List<String> immutableList = list.stream() .collect(ImmutableList.toImmutableList()); System.out.println(immutableList.getClass()); // class com.google.common.collect.RegularImmutableList </pre></td></tr></table></figure><h3 id="不可变集合优点"><a href="#不可变集合优点" class="headerlink" title="不可变集合优点"></a>不可变集合优点</h3><ol><li>当对象被不可信的库调用时，不可变形式是安全的；</li><li>不可变对象被多个线程调用时，不存在竞态条件问题</li><li>不可变集合不需要考虑变化，因此可以节省时间和空间。所有不可变的集合都比它们的可变形式有更好的内存利用率（分析和测试细节）；</li><li>不可变对象因为有固定不变，可以作为常量来安全使用。</li></ol><h2 id="新集合类型"><a href="#新集合类型" class="headerlink" title="新集合类型"></a>新集合类型</h2>Guava提供了许多JDK没有的集合类型。<h3 id="RangeSet"><a href="#RangeSet" class="headerlink" title="RangeSet"></a>RangeSet</h3>RangeSet一组不相连的、非空的区间，基本实现为TreeRangeSet，看个RangeSet的例子：<figure class="highlight java"><table><tr><td class="gutter"><pre>1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 </pre></td><td class="code"><pre>RangeSet<Integer> rangeSet = TreeRangeSet.create(); rangeSet.add(Range.closed(1, 10)); System.out.println(rangeSet); // [[1..10]] rangeSet.add(Range.closedOpen(11, 15)); System.out.println(rangeSet); // 不相连区间 [[1..10], [11..15)] rangeSet.add(Range.closedOpen(15, 20)); System.out.println(rangeSet); // 相连区间 [[1..10], [11..20)] rangeSet.add(Range.openClosed(0, 0)); System.out.println(rangeSet); // 空区间 [[1..10], [11..20)] rangeSet.remove(Range.open(5, 10)); System.out.println(rangeSet); // 区间分割 [[1..5], [10..10], [11..20)] </pre></td></tr></table></figure>查看RangeSet的范围跨度：<figure class="highlight java"><table><tr><td class="gutter"><pre>1 2 3 4 5 6 7 </pre></td><td class="code"><pre>RangeSet<Integer> rangeSet = TreeRangeSet.create(); rangeSet.add(Range.closed(1, 10)); rangeSet.add(Range.closedOpen(11, 15)); Range<Integer> span = rangeSet.span(); System.out.println(span.lowerEndpoint().intValue()); // 1 System.out.println(span.upperEndpoint().intValue()); // 15 </pre></td></tr></table></figure>从已有的RangeSet获取一个子范围RangeSet：<figure class="highlight java"><table><tr><td class="gutter"><pre>1 2 3 4 5 6 7 8 9 </pre></td><td class="code"><pre>RangeSet<Integer> numberRangeSet = TreeRangeSet.create(); numberRangeSet.add(Range.closed(0, 2)); numberRangeSet.add(Range.closed(3, 5)); numberRangeSet.add(Range.closed(5, 8)); RangeSet<Integer> numberSubRangeSet = numberRangeSet.subRangeSet(Range.closed(4, 14)); System.out.println(numberRangeSet); // [[0..2], [3..8]] System.out.println(numberSubRangeSet); // [[4..8]] </pre></td></tr></table></figure>获取除了RangeSet范围外的RangeSet：<figure class="highlight java"><table><tr><td class="gutter"><pre>1 2 3 4 5 6 7 8 9 </pre></td><td class="code"><pre>RangeSet<Integer> numberRangeSet = TreeRangeSet.create(); numberRangeSet.add(Range.closed(0, 2)); numberRangeSet.add(Range.closed(3, 5)); numberRangeSet.add(Range.closed(6, 8)); RangeSet<Integer> numberRangeComplementSet = numberRangeSet.complement(); System.out.println(numberRangeSet); // [[0..2], [3..5], [6..8]] System.out.println(numberRangeComplementSet); // [(-∞..0), (2..3), (5..6), (8..+∞)] </pre></td></tr></table></figure>判断一个RangeSet是否和另一个范围有交集：<figure class="highlight java"><table><tr><td class="gutter"><pre>1 2 3 4 5 6 7 8 </pre></td><td class="code"><pre>RangeSet<Integer> numberRangeSet = TreeRangeSet.create(); numberRangeSet.add(Range.closed(0, 2)); numberRangeSet.add(Range.closed(3, 10)); numberRangeSet.add(Range.closed(15, 18)); System.out.println(numberRangeSet); // [[0..2], [3..10], [15..18]] System.out.println(numberRangeSet.intersects(Range.closed(4, 17))); // true </pre></td></tr></table></figure>遍历RangeSet的范围区间：<figure class="highlight java"><table><tr><td class="gutter"><pre>1 2 3 4 5 6 7 8 </pre></td><td class="code"><pre>RangeSet<Integer> numberRangeSet = TreeRangeSet.create(); numberRangeSet.add(Range.closed(0, 2)); numberRangeSet.add(Range.closed(3, 10)); numberRangeSet.add(Range.closed(15, 18)); Set<Range<Integer>> ranges = numberRangeSet.asRanges(); ranges.forEach(System.out::print); // [0..2][3..10][15..18] </pre></td></tr></table></figure>从RangeSet中获取包含某个值的访问区间：<figure class="highlight java"><table><tr><td class="gutter"><pre>1 2 3 4 5 6 7 </pre></td><td class="code"><pre>RangeSet<Integer> numberRangeSet = TreeRangeSet.create(); numberRangeSet.add(Range.closed(0, 2)); numberRangeSet.add(Range.closed(3, 10)); numberRangeSet.add(Range.closed(15, 18)); System.out.println(numberRangeSet.rangeContaining(7)); // [3..10] </pre></td></tr></table></figure><h3 id="RangeMap"><a href="#RangeMap" class="headerlink" title="RangeMap"></a>RangeMap</h3>RangeMap是一组不相连的、非空的区间与指定值的映射，基本实现为TreeRangeMap光这样说有点抽象，看些例子:<figure class="highlight java"><table><tr><td class="gutter"><pre>1 2 3 4 5 6 7 8 9 10 11 12 </pre></td><td class="code"><pre>RangeMap<Integer, String> rangeMap = TreeRangeMap.create(); rangeMap.put(Range.closed(1, 10), "foo"); System.out.println(rangeMap); // [[1..10]=foo] rangeMap.put(Range.open(3, 6), "bar"); System.out.println(rangeMap); // [[1..3]=foo, (3..6)=bar, [6..10]=foo] rangeMap.put(Range.open(10, 20), "eoo"); System.out.println(rangeMap); // [[1..3]=foo, (3..6)=bar, [6..10]=foo, (10..20)=eoo] rangeMap.remove(Range.closed(5, 11)); System.out.println(rangeMap); // [[1..3]=foo, (3..5)=bar, (11..20)=eoo] </pre></td></tr></table></figure>从RangeMap中获取一个Entry：<figure class="highlight java"><table><tr><td class="gutter"><pre>1 2 3 4 5 6 7 8 9 </pre></td><td class="code"><pre>RangeMap<Integer, String> rangeMap = TreeRangeMap.create(); rangeMap.put(Range.closed(0, 2), "foo"); rangeMap.put(Range.closed(3, 5), "bar"); rangeMap.put(Range.closed(6, 8), "eoo"); Map.Entry<Range<Integer>, String> entry = rangeMap.getEntry(7); System.out.println(entry.getKey()); // [6..8] System.out.println(entry.getValue()); // eoo </pre></td></tr></table></figure>剩下的操作和RangeSet差不多。<h3 id="BiMap"><a href="#BiMap" class="headerlink" title="BiMap"></a>BiMap</h3>BiMap是一种特殊的，双向映射的Map，可以确保不会出现重复的值并且我们总是可以安全地通过key获取到value。BiMap的基本实现为HashBiMap。看看例子：<figure class="highlight java"><table><tr><td class="gutter"><pre>1 2 3 4 5 6 7 8 </pre></td><td class="code"><pre>BiMap<String, String> biMap = HashBiMap.create(); biMap.put("k1", "v1"); biMap.put("k2", "v2"); biMap.put("k3", "v3"); System.out.println(biMap); // {k1=v1, k2=v2, k3=v3} BiMap<String, String> inverse = biMap.inverse(); System.out.println(inverse); // {v1=k1, v2=k2, v3=k3} </pre></td></tr></table></figure>通过<code>inverse</code>可以得到值，键映射的BiMap。往BiMap里添加重复的值将会报错：<figure class="highlight java"><table><tr><td class="gutter"><pre>1 2 3 4 </pre></td><td class="code"><pre>BiMap<String, String> biMap = HashBiMap.create(); biMap.put("k1", "v1"); biMap.put("k2", "v2"); biMap.put("k3", "v1"); </pre></td></tr></table></figure><img src="img/QQ截图20190422172835.png" alt="QQ截图20190422172835.png">如果非要添加重复的值的话，可以用<code>forcePut</code>方法：<figure class="highlight java"><table><tr><td class="gutter"><pre>1 2 3 4 5 </pre></td><td class="code"><pre>BiMap<String, String> biMap = HashBiMap.create(); biMap.put("k1", "v1"); biMap.put("k2", "v2"); biMap.forcePut("k3", "v1"); System.out.println(biMap); // {k2=v2, k3=v1} </pre></td></tr></table></figure><h3 id="Table"><a href="#Table" class="headerlink" title="Table"></a>Table</h3>Table是一个包含行，列和单元格的集合类型，行和列组成有序键对。创建一个HashBasedTable（内部使用LinkedHashMap）：<figure class="highlight java"><table><tr><td class="gutter"><pre>1 </pre></td><td class="code"><pre>Table<String, String, Integer> hashBasedTable = HashBasedTable.create(); </pre></td></tr></table></figure>如果需要对table的行和列按照自然顺序或者提供的排序规则进行排序的话，可以创建一个TreeBasedTable：<figure class="highlight java"><table><tr><td class="gutter"><pre>1 </pre></td><td class="code"><pre>Table<String, String, Integer> treeBasedTable = TreeBasedTable.create(); </pre></td></tr></table></figure>如果事先知道行和列的值，并且table大小是固定的话，可以使用ArrayTable：<figure class="highlight java"><table><tr><td class="gutter"><pre>1 2 3 4 </pre></td><td class="code"><pre>List<String> row = Lists.newArrayList("r1", "r2"); List<String> column = Lists.newArrayList("c1", "c2", "c3"); Table<String, String, Integer> arrayTable = ArrayTable.create(row, column); System.out.println(arrayTable); // {r1={c1=null, c2=null, c3=null}, r2={c1=null, c2=null, c3=null}} </pre></td></tr></table></figure>上面例子创建了一个两行三列的table。创建不可变table：<figure class="highlight java"><table><tr><td class="gutter"><pre>1 2 3 </pre></td><td class="code"><pre>Table<String, String, String> immutableTable = ImmutableTable.<String, String, String> builder() .put("r1", "c1", "hello") .build(); </pre></td></tr></table></figure>通过行和列获取单元格的值：<figure class="highlight java"><table><tr><td class="gutter"><pre>1 2 3 4 5 6 7 8 9 10 11 12 13 </pre></td><td class="code"><pre>Table<String, String, String> hashBasedTable = HashBasedTable.create(); hashBasedTable.put("r1", "c1", "hello"); hashBasedTable.put("r1", "c2", "world"); hashBasedTable.put("r2", "c1", "good"); hashBasedTable.put("r2", "c2", "bye"); System.out.println(hashBasedTable); // {r1={c1=hello, c2=world}, r2={c1=good, c2=bye}} String v1 = hashBasedTable.get("r1", "c1"); String v2 = hashBasedTable.get("r2", "c3"); System.out.println(v1); // hello System.out.println(v2); // null </pre></td></tr></table></figure>我们可以检测table是否包含某个行键，某个列键，某个值和某个行和列组合的键：<figure class="highlight java"><table><tr><td class="gutter"><pre>1 2 3 4 5 6 7 8 9 10 </pre></td><td class="code"><pre>Table<String, String, String> hashBasedTable = HashBasedTable.create(); hashBasedTable.put("r1", "c1", "hello"); hashBasedTable.put("r1", "c2", "world"); hashBasedTable.put("r2", "c1", "good"); hashBasedTable.put("r2", "c2", "bye"); boolean b1 = hashBasedTable.contains("r1", "c2"); // true boolean b2 = hashBasedTable.containsColumn("c3"); // false boolean b3 = hashBasedTable.containsRow("r2"); // true boolean b4 = hashBasedTable.containsValue("world"); // true </pre></td></tr></table></figure>通过行和列删除单元格，返回被删除的值：<figure class="highlight java"><table><tr><td class="gutter"><pre>1 2 3 4 5 6 7 8 9 10 </pre></td><td class="code"><pre>Table<String, String, String> hashBasedTable = HashBasedTable.create(); hashBasedTable.put("r1", "c1", "hello"); hashBasedTable.put("r1", "c2", "world"); hashBasedTable.put("r2", "c1", "good"); hashBasedTable.put("r2", "c2", "bye"); String removeValue = hashBasedTable.remove("r1", "c1"); System.out.println(removeValue); // hello System.out.println(hashBasedTable); // {r1={c2=world}, r2={c1=good, c2=bye}} </pre></td></tr></table></figure>我们可以通过行或列得到一个Map，如果通过行得到Map，那么Map的键为列值，Map的值为对应单元格的值，光说有点抽象，看个例子：<figure class="highlight java"><table><tr><td class="gutter"><pre>1 2 3 4 5 6 7 8 9 10 11 12 </pre></td><td class="code"><pre>Table<String, String, String> hashBasedTable = HashBasedTable.create(); hashBasedTable.put("r1", "c1", "hello"); hashBasedTable.put("r1", "c2", "world"); hashBasedTable.put("r2", "c1", "good"); hashBasedTable.put("r2", "c2", "bye"); Map<String, String> c2Map = hashBasedTable.column("c2"); Map<String, String> r1Map = hashBasedTable.row("r1"); System.out.println(c2Map); // {r1=world, r2=bye} System.out.println(r1Map); // {c1=hello, c2=world} System.out.println(c2Map.get("r1")); // world </pre></td></tr></table></figure>我们还可以单独获取所有行或者所有列组成的Map：<figure class="highlight java"><table><tr><td class="gutter"><pre>1 2 3 4 5 6 7 8 9 10 11 </pre></td><td class="code"><pre>Table<String, String, String> hashBasedTable = HashBasedTable.create(); hashBasedTable.put("r1", "c1", "hello"); hashBasedTable.put("r1", "c2", "world"); hashBasedTable.put("r2", "c1", "good"); hashBasedTable.put("r2", "c2", "bye"); Map<String, Map<String, String>> columnMap = hashBasedTable.columnMap(); Map<String, Map<String, String>> rowMap = hashBasedTable.rowMap(); System.out.println(columnMap); // {c1={r1=hello, r2=good}, c2={r1=world, r2=bye}} System.out.println(rowMap); // {r1={c1=hello, c2=world}, r2={c1=good, c2=bye}} </pre></td></tr></table></figure>获取所有行键、列键或者值的集合：<figure class="highlight java"><table><tr><td class="gutter"><pre>1 2 3 4 5 6 7 8 9 10 11 12 13 </pre></td><td class="code"><pre>Table<String, String, String> hashBasedTable = HashBasedTable.create(); hashBasedTable.put("r1", "c1", "hello"); hashBasedTable.put("r1", "c2", "world"); hashBasedTable.put("r2", "c1", "good"); hashBasedTable.put("r2", "c2", "bye"); Set<String> rowKeySet = hashBasedTable.rowKeySet(); Set<String> columnKeySet = hashBasedTable.columnKeySet(); Set<Table.Cell<String, String, String>> cells = hashBasedTable.cellSet(); System.out.println(rowKeySet); // [r1, r2] System.out.println(columnKeySet); // [c1, c2] System.out.println(cells); // [(r1,c1)=hello, (r1,c2)=world, (r2,c1)=good, (r2,c2)=bye] </pre></td></tr></table></figure><h3 id="Multiset"><a href="#Multiset" class="headerlink" title="Multiset"></a>Multiset</h3>Multiset和java.util.set类似，不过Mutiset可以添加重复的值：<figure class="highlight java"><table><tr><td class="gutter"><pre>1 2 3 4 5 6 7 8 9 10 11 12 </pre></td><td class="code"><pre>HashMultiset<String> hashMultiset = HashMultiset.create(); hashMultiset.add("are you ok?"); hashMultiset.add("are you ok?"); hashMultiset.add("are you ok?"); System.out.println(hashMultiset); // [are you ok? x 3] hashMultiset.remove("are you ok?"); System.out.println(hashMultiset); // [are you ok? x 2] hashMultiset.setCount("are you ok?", 10); // 直接设置元素个数 System.out.println(hashMultiset); // [are you ok? x 10] </pre></td></tr></table></figure>在并发环境下，我们可以使用ConcurrentHashMultiset，它的add和remove方法是线程安全的。唯一值得注意的是，在并发环境下使用setCount方法时候，需使用下面这种方式：<figure class="highlight java"><table><tr><td class="gutter"><pre>1 2 3 4 5 </pre></td><td class="code"><pre>HashMultiset<String> hashMultiset = HashMultiset.create(); hashMultiset.setCount("are you ok?", 0, 5); hashMultiset.setCount("are you ok?", 10, 5); System.out.println(hashMultiset); // [are you ok? x 5] </pre></td></tr></table></figure>第一个参数为需要添加的值，第二个参数为当前Multiset里元素个数，第三个参数为需要添加的元素个数。只有第二个参数的值正确的时候，setCount才有效，所以<code>hashMultiset.setCount("are you ok?", 10, 5)</code>实际上是不生效的。<h3 id="Multimap"><a href="#Multimap" class="headerlink" title="Multimap"></a>Multimap</h3>Multimap可以通过一个键映射多个值：<figure class="highlight java"><table><tr><td class="gutter"><pre>1 2 3 4 5 6 7 </pre></td><td class="code"><pre>String key = "hello"; ArrayListMultimap<String, String> multimap = ArrayListMultimap.create(); multimap.put(key, "world"); multimap.put(key, "java"); System.out.println(multimap); // {hello=[world, java]} System.out.println(multimap.get(key)); // [world, java] </pre></td></tr></table></figure><h3 id="ClassToInstanceMap"><a href="#ClassToInstanceMap" class="headerlink" title="ClassToInstanceMap"></a>ClassToInstanceMap</h3>使用类型作为键：<figure class="highlight java"><table><tr><td class="gutter"><pre>1 2 3 4 5 6 7 </pre></td><td class="code"><pre>MutableClassToInstanceMap<Object> classToInstanceMap = MutableClassToInstanceMap.create(); classToInstanceMap.put(String.class, "hello"); classToInstanceMap.put(Integer.class, 777); classToInstanceMap.put(Double.class, 43.96); System.out.println(classToInstanceMap); // {class java.lang.Double=43.96, class java.lang.String=hello, class java.lang.Integer=777} System.out.println(classToInstanceMap.get(Double.class)); // 43.96 </pre></td></tr></table></figure><h2 id="Lists、Maps-amp-Sets"><a href="#Lists、Maps-amp-Sets" class="headerlink" title="Lists、Maps&Sets"></a>Lists、Maps&Sets</h2><h3 id="Lists"><a href="#Lists" class="headerlink" title="Lists"></a>Lists</h3>创建一个List：<figure class="highlight java"><table><tr><td class="gutter"><pre>1 </pre></td><td class="code"><pre>ArrayList<String> list = Lists.newArrayList("a", "b", "c"); </pre></td></tr></table></figure>反转List：<figure class="highlight java"><table><tr><td class="gutter"><pre>1 2 3 4 </pre></td><td class="code"><pre>ArrayList<String> list = Lists.newArrayList("a", "b", "c"); List<String> reverse = Lists.reverse(list); System.out.println(reverse); // [c, b, a] </pre></td></tr></table></figure>通过字符串生成字符集合：<figure class="highlight java"><table><tr><td class="gutter"><pre>1 2 </pre></td><td class="code"><pre>List<Character> characters = Lists.charactersOf("mrbird"); System.out.println(characters); // [m, r, b, i, r, d] </pre></td></tr></table></figure>将集合按照指定区块大小分区：<figure class="highlight java"><table><tr><td class="gutter"><pre>1 2 3 4 </pre></td><td class="code"><pre>List<String> list = Lists.newArrayList("java", "php", "go", "python", "c#", "javascript"); List<List<String>> partition = Lists.partition(list, 2); System.out.println(partition); // [[java, php], [go, python], [c#, javascript]] </pre></td></tr></table></figure>一个删除List中重复项的技巧：<figure class="highlight java"><table><tr><td class="gutter"><pre>1 2 3 4 </pre></td><td class="code"><pre>List<String> list = Lists.newArrayList("a", "p", "p", "l", "e"); ImmutableList<String> newList = ImmutableSet.copyOf(list).asList(); System.out.println(newList); // [a, p, l, e] </pre></td></tr></table></figure>从集合中删除null值：<figure class="highlight java"><table><tr><td class="gutter"><pre>1 2 3 4 </pre></td><td class="code"><pre>List<String> list = Lists.newArrayList("java", null," python"); Iterables.removeIf(list, Objects::isNull); System.out.println(list); // [java, python] </pre></td></tr></table></figure><h3 id="Sets"><a href="#Sets" class="headerlink" title="Sets"></a>Sets</h3>通过Sets创建set：<figure class="highlight java"><table><tr><td class="gutter"><pre>1 </pre></td><td class="code"><pre>Set<Object> hashSet = Sets.newHashSet(); </pre></td></tr></table></figure>合并两个Set：<figure class="highlight java"><table><tr><td class="gutter"><pre>1 2 3 4 5 </pre></td><td class="code"><pre>Set<String> set1 = ImmutableSet.of("a", "b", "c"); Set<String> set2 = ImmutableSet.of("b", "c", "d"); Set<String> union = Sets.union(set1, set2); System.out.println(union); // [a, b, c, d] </pre></td></tr></table></figure>可以通过<code>Sets.cartesianProduct()</code>获取两个Set的笛卡尔积：<figure class="highlight java"><table><tr><td class="gutter"><pre>1 2 3 4 5 </pre></td><td class="code"><pre>Set<Character> first = ImmutableSet.of('a', 'b'); Set<Character> second = ImmutableSet.of('c', 'd'); Set<List<Character>> result = Sets.cartesianProduct(first, second); System.out.println(result); // [[a, c], [a, d], [b, c], [b, d]] </pre></td></tr></table></figure>获取两个Set的交集：<figure class="highlight java"><table><tr><td class="gutter"><pre>1 2 3 4 5 </pre></td><td class="code"><pre>Set<Character> first = ImmutableSet.of('a', 'b', 'c'); Set<Character> second = ImmutableSet.of('c', 'd', 'e'); Set<Character> intersection = Sets.intersection(first, second); System.out.println(intersection); // [c] </pre></td></tr></table></figure>获取两个Set的差集：<figure class="highlight java"><table><tr><td class="gutter"><pre>1 2 3 4 5 </pre></td><td class="code"><pre>Set<Character> first = ImmutableSet.of('a', 'b', 'c'); Set<Character> second = ImmutableSet.of('c', 'd', 'e'); Set<Character> difference = Sets.symmetricDifference(first, second); System.out.println(difference); // [a, b, d, e] </pre></td></tr></table></figure><h3 id="Maps"><a href="#Maps" class="headerlink" title="Maps"></a>Maps</h3>通过Maps创建Map：<figure class="highlight java"><table><tr><td class="gutter"><pre>1 </pre></td><td class="code"><pre>HashMap<Object, Object> map = Maps.newHashMap(); </pre></td></tr></table></figure>创建期望大小的Map：<figure class="highlight java"><table><tr><td class="gutter"><pre>1 </pre></td><td class="code"><pre>HashMap<Object, Object> map = Maps.newHashMapWithExpectedSize(5); </pre></td></tr></table></figure><h2 id="Joiner与Splitter"><a href="#Joiner与Splitter" class="headerlink" title="Joiner与Splitter"></a>Joiner与Splitter</h2><h3 id="Joiner"><a href="#Joiner" class="headerlink" title="Joiner"></a>Joiner</h3>Joiner用于连接操作。比如将List里的元素通过“,”连接成一个字符串：<figure class="highlight java"><table><tr><td class="gutter"><pre>1 2 3 4 </pre></td><td class="code"><pre>List<String> list = Lists.newArrayList("a", "b", "c"); String join = Joiner.on(",").join(list); System.out.println(join); // a,b,c </pre></td></tr></table></figure>使用Joiner将Map转换为String：<figure class="highlight java"><table><tr><td class="gutter"><pre>1 2 3 4 5 6 </pre></td><td class="code"><pre>HashMap<String, Integer> map = Maps.newHashMap(); map.put("mrbird", 18); map.put("scott", 28); String join = Joiner.on(",").withKeyValueSeparator("~").join(map); System.out.println(join); // mrbird~18,scott~28 </pre></td></tr></table></figure>在使用Joiner的时候，如果集合中含有null值，我们可以选择跳过它：<figure class="highlight java"><table><tr><td class="gutter"><pre>1 2 3 4 </pre></td><td class="code"><pre>List<String> list = Lists.newArrayList("a", null, "b", "c", "d"); String result = Joiner.on(",").skipNulls().join(list); System.out.println(result); // a,b,c,d </pre></td></tr></table></figure>或者使用指定值替代null：<figure class="highlight java"><table><tr><td class="gutter"><pre>1 2 3 4 </pre></td><td class="code"><pre>List<String> list = Lists.newArrayList("a", null, "b", "c", "d"); String result = Joiner.on(",").useForNull("空").join(list); System.out.println(result); // a,空,b,c,d </pre></td></tr></table></figure><h3 id="Splitter"><a href="#Splitter" class="headerlink" title="Splitter"></a>Splitter</h3>Splitter用于将String拆分为集合类型，看个例子:<figure class="highlight java"><table><tr><td class="gutter"><pre>1 2 3 4 </pre></td><td class="code"><pre>String value = "a,b,c,d "; List<String> list = Splitter.on(",").trimResults().splitToList(value); System.out.println(list); // [a, b, c, d] </pre></td></tr></table></figure>使用Splitter将String拆分为Map：<figure class="highlight java"><table><tr><td class="gutter"><pre>1 2 3 4 </pre></td><td class="code"><pre> String value = "mrbird=18,scott=28"; Map<String, String> map = Splitter.on(",").withKeyValueSeparator("=").split(value); System.out.println(map); // {mrbird=18, scott=28} </pre></td></tr></table></figure>分割具有多种分隔符的String：<figure class="highlight java"><table><tr><td class="gutter"><pre>1 2 3 4 </pre></td><td class="code"><pre>String value = "a.b,,c,,.."; List<String> result = Splitter.onPattern("[.,]").omitEmptyStrings().splitToList(value); System.out.println(result); // [a, b, c] </pre></td></tr></table></figure><code>omitEmptyStrings</code>用于忽略空字符串。我们还可以通过指定长度来拆分字符串：<figure class="highlight java"><table><tr><td class="gutter"><pre>1 2 3 4 </pre></td><td class="code"><pre>String value = "人们都说：“桂林山水甲天下”，我们乘着木船荡漾在漓江上，来观赏桂林的山水。"; List<String> list = Splitter.fixedLength(3).splitToList(value); System.out.println(list); // [人们都, 说：“, 桂林山, 水甲天, 下”，, 我们乘, 着木船, 荡漾在, 漓江上, ，来观, 赏桂林, 的山水, 。] </pre></td></tr></table></figure>也可以指定拆分项的长度：<figure class="highlight java"><table><tr><td class="gutter"><pre>1 2 3 4 </pre></td><td class="code"><pre>String value = "a-b-c-d-e"; List<String> result = Splitter.on("-").limit(4).splitToList(value); System.out.println(result); // [a, b, c, d-e] </pre></td></tr></table></figure>可以看到d-e没有被拆分。<h2 id="Filter-amp-Transform"><a href="#Filter-amp-Transform" class="headerlink" title="Filter&Transform"></a>Filter&Transform</h2><h3 id="Filter"><a href="#Filter" class="headerlink" title="Filter"></a>Filter</h3>可以通过Guava提供的Predicates来实现各种集合过滤操作。比如找出集合中包含a的元素：<figure class="highlight java"><table><tr><td class="gutter"><pre>1 2 3 4 </pre></td><td class="code"><pre>List<String> list = Lists.newArrayList("java", "javascript", "c#", "golang"); Iterable<String> result = Iterables.filter(list, Predicates.containsPattern("a")); System.out.println(result); // [java, javascript, golang] </pre></td></tr></table></figure>上面的例子也可以通过<code>Collections2.filter</code>来实现：<figure class="highlight java"><table><tr><td class="gutter"><pre>1 2 3 4 </pre></td><td class="code"><pre>List<String> list = Lists.newArrayList("java", "javascript", "c#", "golang"); Collection<String> result = Collections2.filter(list, Predicates.containsPattern("a")); System.out.println(result); </pre></td></tr></table></figure>我们也可以编写自定义的过滤规则：<figure class="highlight java"><table><tr><td class="gutter"><pre>1 2 3 4 5 6 7 8 9 10 11 12 13 14 </pre></td><td class="code"><pre> Predicate<String> predicate = new Predicate<String>() { @Override public boolean apply(@Nullable String input) { return input.endsWith("a") || input.contains("#"); } @Override public boolean test(String input) { return this.apply(input); } }; List<String> list = Lists.newArrayList("java", "javascript", "c#", "golang"); Collection<String> result = Collections2.filter(list, predicate); System.out.println(result); // [java, c#] </pre></td></tr></table></figure>组合多个过滤条件：<figure class="highlight java"><table><tr><td class="gutter"><pre>1 2 3 4 5 6 7 </pre></td><td class="code"><pre>List<String> list = Lists.newArrayList("java", "javascript", "c#", "golang"); Collection<String> result = Collections2.filter(list, Predicates.or( Predicates.containsPattern("a"), Predicates.containsPattern("#") )); System.out.println(result); // [java, javascript, c#, golang] </pre></td></tr></table></figure>过滤掉集合中的null：<figure class="highlight java"><table><tr><td class="gutter"><pre>1 2 3 4 </pre></td><td class="code"><pre>List<String> list = Lists.newArrayList("java", null," python"); Collection<String> result = Collections2.filter(list, Predicates.<String>notNull()); System.out.println(result); // [java, python] </pre></td></tr></table></figure>检测集合中是否有包含a字符的元素：<figure class="highlight java"><table><tr><td class="gutter"><pre>1 2 3 4 </pre></td><td class="code"><pre>List<String> list = Lists.newArrayList("java", "c#"," python"); boolean result = Iterables.any(list, Predicates.containsPattern("a")); System.out.println(result); // true </pre></td></tr></table></figure><h3 id="Transform"><a href="#Transform" class="headerlink" title="Transform"></a>Transform</h3>将集合转换为元素长度的集合：<figure class="highlight java"><table><tr><td class="gutter"><pre>1 2 3 4 5 6 7 8 9 10 11 </pre></td><td class="code"><pre>Function<String, Integer> function = new Function<String, Integer>() { @Nullable @Override public Integer apply(@Nullable String s) { return s.length(); } }; List<String> list = Lists.newArrayList("java", "c#", " python"); Iterable<Integer> result = Iterables.transform(list, function); System.out.println(result); // [4, 2, 7] </pre></td></tr></table></figure>上面的例子同样可以使用<code>Collections2.transform</code>来代替<code>Iterables.transform</code>。我们也可以通过<code>Functions.forPredicate</code>来创建简单的转换函数Function：<figure class="highlight java"><table><tr><td class="gutter"><pre>1 2 3 4 </pre></td><td class="code"><pre>List<String> list = Lists.newArrayList("java", "c#", " python"); Iterable<Boolean> result = Iterables.transform(list, Functions.forPredicate(Predicates.containsPattern("#"))); System.out.println(result); // [false, true, false] </pre></td></tr></table></figure>组合多个转换函数：<figure class="highlight java"><table><tr><td class="gutter"><pre>1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 </pre></td><td class="code"><pre>Function<String, String> f1 = new Function<String, String>() { @Override public String apply(String input) { return "i like " + input; } }; Function<String, String> f2 = new Function<String, String>() { @Override public String apply(String input) { return input.toUpperCase(); } }; List<String> list = Lists.newArrayList("java", "c#", " python"); Iterable<String> result = Iterables.transform(list, Functions.compose(f2, f1)); System.out.println(result); // [I LIKE JAVA, I LIKE C#, I LIKE PYTHON] </pre></td></tr></table></figure>我们也可以将过滤和转换组合在一起使用：<figure class="highlight java"><table><tr><td class="gutter"><pre>1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 </pre></td><td class="code"><pre>Predicate<String> predicate = new Predicate<String>() { @Override public boolean apply(String input) { return input.startsWith("j"); } @Override public boolean test(String input) { return this.apply(input); } }; Function<String, String> function = new Function<String,String>(){ @Override public String apply(String input) { return input.toUpperCase(); } }; List<String> list = Lists.newArrayList("java", "c#", "javascript", "python"); ImmutableList<String> result = FluentIterable.from(list) .filter(predicate) .transform(function) .toList(); System.out.println(result); // [JAVA, JAVASCRIPT] </pre></td></tr></table></figure><h2 id="Iterables"><a href="#Iterables" class="headerlink" title="Iterables"></a>Iterables</h2>除了上面涉及的Iterables的用法外，其还提供了许多别的好用的方法。<h3 id="removeAll"><a href="#removeAll" class="headerlink" title="removeAll"></a>removeAll</h3>该方法用于从特定集合中删除给定集合中的元素：<figure class="highlight java"><table><tr><td class="gutter"><pre>1 2 3 4 5 6 </pre></td><td class="code"><pre>List<String> removeFrom = Lists.newArrayList("a", "b", "c"); List<String> elementsToRemove = Lists.newArrayList("b", "c"); boolean result = Iterables.removeAll(removeFrom, elementsToRemove); System.out.println(result); // true System.out.println(removeFrom); // [a] </pre></td></tr></table></figure><h3 id="retainAll"><a href="#retainAll" class="headerlink" title="retainAll"></a>retainAll</h3>retainAll的功能和removeAll相反：<figure class="highlight java"><table><tr><td class="gutter"><pre>1 2 3 4 5 6 </pre></td><td class="code"><pre>List<String> removeFrom = Lists.newArrayList("a", "b", "c"); List<String> elementsToRetain = Lists.newArrayList("b", "c"); boolean result = Iterables.retainAll(removeFrom, elementsToRetain); System.out.println(result); // true System.out.println(removeFrom); // [b, c] </pre></td></tr></table></figure><h3 id="addAll"><a href="#addAll" class="headerlink" title="addAll"></a>addAll</h3>addAll用于将给定集合添加到现有集合中：<figure class="highlight java"><table><tr><td class="gutter"><pre>1 2 3 4 5 </pre></td><td class="code"><pre>List<String> list1 = Lists.newArrayList("a", "b", "c"); List<String> list2 = Lists.newArrayList("b", "c"); boolean b = Iterables.addAll(list1, list2); // true System.out.println(list1); // [a, b, c, b, c] </pre></td></tr></table></figure><h3 id="concat"><a href="#concat" class="headerlink" title="concat"></a>concat</h3>concat用于合并集合，组成一个新的集合对象：<figure class="highlight java"><table><tr><td class="gutter"><pre>1 2 3 4 5 </pre></td><td class="code"><pre>List<String> list1 = Lists.newArrayList("a", "b", "c"); List<String> list2 = Lists.newArrayList("b", "c"); Iterable<String> result = Iterables.concat(list1,list2); System.out.println(result); // [a, b, c, b, c] </pre></td></tr></table></figure>Iterables还包含许多别的实用方法：<img src="img/QQ截图20190423231111.png" alt="QQ截图20190423231111.png">这里就不一一演示了，溜了。<img src="img/QQ图片20190423231252.png" alt="QQ图片20190423231252.png">更详细的内容可以参考guava官方wiki：<a href="https://github.com/google/guava/wiki" target="_blank" rel="noopener">https://github.com/google/guava/wiki</a><script>$(".post-body a").not(".thispage").addClass("ignore-href").attr("target","_blank")</script></div><div></div><div><div style="padding:10px 0;margin:20px auto;width:90%;text-align:center;color:#878787" id="reward-div"><div>请作者喝瓶肥宅水🥤</div><button id="rewardButton" style="margin-top:10px" disable="enable" onclick='var e=document.getElementById("QR");"none"===e.style.display?e.style.display="block":e.style.display="none"'>￥</button><div id="QR" style="display:none"><div id="wechat" style="display:inline-block"><img id="wechat_qr" src="/img/wechat_pay.png" alt="MrBird WeChat Pay"></div><div id="alipay" style="display:inline-block"><img id="alipay_qr" src="/img/ali_pay.png" alt="MrBird 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itemprop="name">MrBird</div>A simple blog, code repository, just keep blogging</div><div class="author__count"><a href="/archives" class="ignore-href">14 Archives </a><a href="/tags" class="ignore-href">2 Labels</a></div></div><div class="author__urls-wrapper"><ul class="author__urls social-icons"><li><a href="/" itemprop="url" class="ignore-href">🏠 Home</a></li><li><a href="/archives" itemprop="url" class="ignore-href">📦 Archives</a></li><li><a href="/tags" itemprop="url" class="ignore-href">🔖 Labels</a></li><li><a href="/friends" itemprop="url" class="ignore-href">👬 Friends</a></li><li><a href="javascript:;" class="popup-trigger animsition-link">🔍 Search</a></li></ul></div></div></div></section><section class="post-toc-wrap motion-element sidebar-panel sidebar-panel-active"><div class="post-toc"><div class="post-toc-content"><ol class="nav"><li class="nav-item nav-level-2"><a class="nav-link" href="#不可变集合">1. 不可变集合</a><ol class="nav-child"><li class="nav-item nav-level-3"><a class="nav-link" href="#创建不可变集合">1.1. 创建不可变集合</a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#不可变集合优点">1.2. 不可变集合优点</a></li></ol></li><li class="nav-item nav-level-2"><a class="nav-link" href="#新集合类型">2. 新集合类型</a><ol class="nav-child"><li class="nav-item nav-level-3"><a class="nav-link" href="#RangeSet">2.1. RangeSet</a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#RangeMap">2.2. RangeMap</a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#BiMap">2.3. BiMap</a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#Table">2.4. Table</a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#Multiset">2.5. Multiset</a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#Multimap">2.6. Multimap</a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#ClassToInstanceMap">2.7. ClassToInstanceMap</a></li></ol></li><li class="nav-item nav-level-2"><a class="nav-link" href="#Lists、Maps-amp-Sets">3. Lists、Maps&Sets</a><ol class="nav-child"><li class="nav-item nav-level-3"><a class="nav-link" href="#Lists">3.1. Lists</a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#Sets">3.2. Sets</a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#Maps">3.3. Maps</a></li></ol></li><li class="nav-item nav-level-2"><a class="nav-link" href="#Joiner与Splitter">4. Joiner与Splitter</a><ol class="nav-child"><li class="nav-item nav-level-3"><a class="nav-link" href="#Joiner">4.1. Joiner</a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#Splitter">4.2. Splitter</a></li></ol></li><li class="nav-item nav-level-2"><a class="nav-link" href="#Filter-amp-Transform">5. Filter&Transform</a><ol class="nav-child"><li class="nav-item nav-level-3"><a class="nav-link" href="#Filter">5.1. Filter</a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#Transform">5.2. Transform</a></li></ol></li><li class="nav-item nav-level-2"><a class="nav-link" href="#Iterables">6. 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