如何判断list map集合中是否存在某个元素

1.在list中判断是是否存在相同元素。
用list的 contains(Object o) 方法
web

2.list集合中去重svg

代码：3d

public static void main(String[] args) {
			
			Student stu1 = new Student("张三", 5);
			Student stu2 = new Student("李四", 5);
			Student stu3 = new Student("王五", 5);
			
			List<Student> stuList = new ArrayList<Student>();
			List<Student> stuList2 = new ArrayList<Student>();
			stuList.add(stu1);
			stuList.add(stu2);
			stuList.add(stu1);
			for(int i=0;i<stuList.size();i++){
				//不包含则加入
				if(!stuList2.contains(stuList.get(i))){
					stuList2.add(stuList.get(i));
				}
			}
			System.out.println(stuList.contains(stu1));
			System.out.println(stuList.contains(stu3));
			System.out.println(stuList);
			System.out.println(stuList2);
			
		}

结果：code

3.Map集合是否包含指定的Key和Value containsKey() containsValue()
在Map中，用containsKey()方法，判断是否包含某个Key值；用containsValue()方法，判断是否包含某个Value值。xml

举个例子blog

public static void main(String[] args) {

		Student stu1 = new Student("张三", 5);
		Student stu2 = new Student("李四", 5);
		Student stu3 = new Student("王五", 5);
		
		Map<String,Student> result = new HashMap<String, Student>();
		result.put("1", stu1);
		result.put("3", stu2);
		
		System.out.println(result.containsKey("1"));
		System.out.println(result.containsKey("2"));
		System.out.println(result.containsValue(stu1));
		System.out.println(result.containsValue(stu3));
	}

结果：
图片