Java集合遍历
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目录
List集合遍历 方式一、使用普通for循环遍历 1 2 3 4 5 6 7 8 List<String> items = new ArrayList<>(); items.add("A" ); items.add("B" ); items.add("C" );int itemsSize = items.size();for (int i = 0 ; i < itemsSize; i++) { System.out.println(items.get(i)); }
方式二、使用增强for循环遍历 1 2 3 4 5 6 7 List<String> items = new ArrayList<>(); items.add("A" ); items.add("B" ); items.add("C" );for (String item : items) { System.out.println(item); }
方式三、使用Lambda表达式forEach遍历(JDK1.8) 1 2 3 4 5 6 7 8 List<String> items = new ArrayList<>(); items.add("A" ); items.add("B" ); items.add("C" ); items.forEach(item -> System.out.println(item)); items.forEach(System.out::println);
Map集合遍历 方式一、通过Map.keySet使用iterator遍历 1 2 3 4 5 6 7 8 9 10 Map<Integer, String> map = new HashMap<>(); map.put(1 , "A" ); map.put(2 , "B" ); map.put(3 , "C" ); Iterator<Integer> iterator = map.keySet().iterator();while (iterator.hasNext()) { Integer key = iterator.next(); String value = map.get(key); System.out.println("key = " + key + ", value = " + value); }
方式二、通过Map.entrySet使用iterator遍历 1 2 3 4 5 6 7 8 9 10 Map<Integer, String> map = new HashMap<>(); map.put(1 , "A" ); map.put(2 , "B" ); map.put(3 , "C" ); System.out.println(map); Iterator<Map.Entry<Integer, String>> entries = map.entrySet().iterator();while (entries.hasNext()) { Map.Entry<Integer, String> entry = entries.next(); System.out.println(entry); }
结果:
1 2 3 4 {1 =A, 2 =B, 3 =C}1 =A2 =B3 =C
方式三、使用Map.keySet遍历 1 2 3 4 5 6 7 Map<Integer, String> map = new HashMap<>(); map.put(1 , "A" ); map.put(2 , "B" ); map.put(3 , "C" );for (Integer key : map.keySet()) { System.out.println("key = " + key + ", value = " + map.get(key)); }
方式四、使用Map.entrySet遍历 1 2 3 4 5 6 7 Map<Integer, String> map = new HashMap<>(); map.put(1 , "A" ); map.put(2 , "B" ); map.put(3 , "C" );for (Map.Entry<Integer, String> entry : map.entrySet()) { System.out.println("key = " + entry.getKey() + ", value = " + entry.getValue()); }
方式五、使用Lambda表达式forEach遍历(JDK1.8) 1 2 3 4 5 Map<Integer, String> map = new HashMap<>(); map.put(1 , "A" ); map.put(2 , "B" ); map.put(3 , "C" ); map.forEach((k, v) -> System.out.println("key = " + k + ", value = " + v));