Java笔记(3)

 ArrayList<String> list = new ArrayList<>();

 ListIterator<String> iterator = list.listIterator();
         while (iterator.hasNext()){
             String s = iterator.next();
             if(s.equals("b")){
                 iterator.remove();//iterator.add("qqq");
             }
             System.out.println(s);
         }

 Set<String>set1=new HashSet<>();
 Set<String> set = list.stream().collect(Collectors.toSet());

         //创建Map集合对象
         Map<String,String> m = new HashMap<>();
         //添加元素
         //put 添加和覆盖
         //如果键不存在则添加,返回null
         // 如果键存在则覆盖,并把原有的数据返回
         m.put("Leo","Ann");
         m.put("Luck","Lucy");
         String s = m.put("Anna","Lucy");
         System.out.println(s);//原数据中没有anna，所以返回null
 ​
         String s1 = m.put("Luck","Fuck");
         System.out.println(s1);
 ​
         String result = m.remove("Leo");
         System.out.println(result);
         //删除返回被删除的值
         String s2 = m.remove("Luck");
         System.out.println(s2);
         //判断键是否存在
         boolean valueResult = m.containsValue("Lucy");
         System.out.println(valueResult);
         boolean isResult = m.isEmpty();
         if(isResult){
             System.out.println("集合为空");
         }else{
             System.out.println("集合不为空");
         }
         System.out.println(m);
 ​
         Map<String,String>map = new HashMap<>();
         map.put("Leo","Ann");
         map.put("Luck","Lucy");
         map.put("Anna","Lucy");
 ​
         Set<String> keys = map.keySet();
 ​
         //增强for循环遍历
         for (String key : keys) {
             System.out.println(key);
             String value = map.get(key);
             System.out.println(key+"="+value);
         }
 ​
         //lambda表达式遍历
         map.keySet().forEach(key->{
             System.out.println(key);
             String value = map.get(key);
             System.out.println(key+"="+value);
         });
 ​
         //迭代器遍历
         Iterator<String> it = map.keySet().iterator();
         while(it.hasNext()){
             String key = it.next();
             System.out.println(key);
             String value = map.get(key);
             System.out.println(key+"="+value);
         }
 ​
         //增强for循环遍历
         Set<Map.Entry<String,String>> entrySet = map.entrySet();
         for (Map.Entry<String,String> entry : entrySet) {
             String key = entry.getKey();
             String value = entry.getValue();
             System.out.println(key+"="+value);
         }
 ​
         for(Map.Entry<String,String> entry : map.entrySet()){
             String key = entry.getKey();
             String value = entry.getValue();
             System.out.println(key+"="+value);
         }
 ​
         //lambda表达式遍历
         map.forEach(new BiConsumer<String, String>() {
             @Override
             public void accept(String key, String value) {
                 System.out.println(key + "=" + value);
             }
         });
         System.out.println("---------------------");
         map.forEach((String key,String value)->{
             System.out.println(key+"="+value);
         });