Java遍历集合(List,Map)

遍历List

public void iteratorList(){
        List<String> list = new ArrayList<>();
        list.add("a");
        list.add("b");
        //方法1 使用iterator遍历
        Iterator<String> iterator = list.iterator();
        while (iterator.hasNext()){
            String value = iterator.next();
            System.out.println(value);
        }
        //方法2 传统for循环
        for(int i=0;i<list.size();i++){
            String value = list.get(i);
            System.out.println(value);
        }
        //方法3 增强for循环
        for(String str : list){
            System.out.println(str);
        }
    }

遍历Map

public void iteratorMap(){
        Map<String,String> map = new HashMap<>();
        map.put("1","a");
        map.put("2","b");
        //方法1 传统遍历集合方法 keySet
        //取key的set
        Set<String> set1 = map.keySet();
        //取迭代器遍历对应的值
        Iterator<String> it1 = set1.iterator();
        while (it1.hasNext()){
            String key = it1.next();
            String value = map.get(key);
            System.out.println(key + ":" + value);
        }

        //方法2 传统遍历集合方法 entrySet
        Set<Map.Entry<String,String>> set2 = map.entrySet();
        //取得迭代器遍历出对应的值
        Iterator<Map.Entry<String,String>> it2 = set2.iterator();
        while(it2.hasNext()){
            Map.Entry<String,String> entry = it2.next();
            String key = entry.getKey();
            String value = entry.getValue();
            System.out.println(key + ":" + value);
        }

        //方法3 增强for循环遍历map集合 keySet
        Set<String> set3 = map.keySet();
        for(String str : set3){
            String key = str;
            String value = map.get(key);
            System.out.println(key + ":" + value);
        }
        //方法4 增强for循环遍历map集合 entySet
        Set<Map.Entry<String,String>> set4 = map.entrySet();
        for(Map.Entry<String,String> entry : set4){
            String key = entry.getKey();
            String value = entry.getValue();
            System.out.println(key + ":" + value);
        }
    }