java集合类四-TreeSet与TreeMap的使用

目录

 

1 TreeSet实现自动排序

2 TreeMap实现自动排序

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1 TreeSet实现自动排序

    @Test
    public void testCalculate() {
        Student stu1 = new Student("张三", 80);
        Student stu2 = new Student("李四", 60);
        Student stu3 = new Student("王二", 90);
        Student stu4 = new Student("麻子", 70);
        // 定义排序类型，按照分数排序
        TreeSet<Student> stuSet = new TreeSet<>(Comparator.comparingInt(Student::getScore));

        //添加数据的时候排序
        stuSet.add(stu1);
        stuSet.add(stu2);
        stuSet.add(stu3);
        stuSet.add(stu4);
        for(Student stu: stuSet){
            System.out.println(stu);
        }
        System.out.println("******************************");
        //更改数据不会影响原来的顺序，TreeSet使用的时候最好不要修改数据
        stu4.setScore(95);
        for(Student stu: stuSet){
            System.out.println(stu);
        }
    }

测试结果

Student(name=李四, score=60)
Student(name=麻子, score=70)
Student(name=张三, score=80)
Student(name=王二, score=90)
******************************
Student(name=李四, score=60)
Student(name=麻子, score=95)
Student(name=张三, score=80)
Student(name=王二, score=90)

2 TreeMap实现自动排序

    @Test
    public void testCalculate() {
        Student stu1 = new Student("张三", 80);
        Student stu2 = new Student("李四", 60);
        Student stu3 = new Student("王二", 90);
        Student stu4 = new Student("麻子", 70);
        TreeMap<Student, String> stuMap = new TreeMap<>(Comparator.comparingInt(Student::getScore));

        //添加数据的时候排序
        stuMap.put(stu1, "");
        stuMap.put(stu2, "");
        stuMap.put(stu3, "");
        stuMap.put(stu4, "");
        for (Student student : stuMap.keySet()) {
            System.out.println(student);
        }
        System.out.println("******************************");
        //更改数据不会影响原来的顺序，TreeMap使用的时候最好不要修改数据
        stu4.setScore(95);
        for (Student student : stuMap.keySet()) {
            System.out.println(student);
        }
    }

测试结果：

Student(name=李四, score=60)
Student(name=麻子, score=70)
Student(name=张三, score=80)
Student(name=王二, score=90)
******************************
Student(name=李四, score=60)
Student(name=麻子, score=95)
Student(name=张三, score=80)
Student(name=王二, score=90)