Collections集合工具类的方法

     ArrayList<String> list=new ArrayList<>();
        Collections.addAll(list,"a","b","c","d","1","aaa");
        System.out.println(list);
        Collections.shuffle(list);
        System.out.println(list);

Collections集合工具类的方法1

package com.mujiachao;

import java.util.Objects;

public class Person implements Comparable<Person> {

    private String name;
    private Integer age;

    public Person() {
    }

    public Person(String name, Integer age) {
        this.name = name;
        this.age = age;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        Person person = (Person) o;
        return Objects.equals(name, person.name) &&
                Objects.equals(age, person.age);
    }

    @Override
    public int hashCode() {

        return Objects.hash(name, age);
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    @Override
    public String toString() {
        return "Person{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }

    @Override
    public int compareTo(Person o) {
        //升序
        return this.getAge()-o.getAge();
        //降序
//        return o.getAge()-this.getAge();
    }
}

        Person p1 = new Person("张三", 12);
        Person p2 = new Person("李四", 8);
        Person p3 = new Person("王五", 72);
        Person p4 = new Person("赵柳", 15);
        Collections.addAll(person,p1,p2,p3,p4);
        Collections.sort(person);
        System.out.println(person);

实现Comparable接口 重写compareTo（）方法

Collections集合工具类的方法2

package com.mujiachao;

public class Student {
    private String name;
    private Integer age;

    public Student() {
    }

    public Student(String name, Integer age) {
        this.name = name;
        this.age = age;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    @Override
    public String toString() {
        return "Student{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
}

public static void main(String[] args) {
        ArrayList<Student> students=new ArrayList<>();
        Student p1 = new Student("张三", 12);
        Student p2 = new Student("a李四", 8);
        Student p3 = new Student("b王五", 8);
        Student p4 = new Student("赵柳", 15);
        Collections.addAll(students,p1,p2,p3,p4);
        Collections.sort(students, new Comparator<com.mujiachao.Student>() {
            @Override
            public int compare(Student o1, Student o2) {
                int result=o1.getAge()-o2.getAge();
                if (result == 0) {
                    result=o1.getName().charAt(0)-o2.getName().charAt(0);
                }
                return result;
            }
        });
        System.out.println(students);
    }

Collections集合工具类的方法3