集合工具类Collections_集合工具类 csdn-优快云博客

本文链接：https://blog.youkuaiyun.com/qq_34577961/article/details/127641158

本文介绍了Java中可变参数的使用方法，演示了如何通过可变参数传递不同数量的参数给方法。此外，还详细讲解了Java集合框架下Collections类的常用API，包括列表的初始化、排序及自定义排序等操作。

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可变参数

public class Test {
    public static void main(String[] args) {
        sum();
        sum(19);
        sum(19,20);
        sum(new int[]{19,20});
    }
    public static  void  sum(int...nums){
        System.out.println("sum接收的是数组,可接收0，1，多个参数，且一个方法只能一个可变参数，且要放在最后面" + Arrays.toString(nums));
        
    }
}

Collections常用api

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

public class Test {
    public static void main(String[] args) {
        List<Integer> list = new ArrayList<>();
        Collections.addAll(list ,11,2,3,41,5); //添加多个值
        Collections.shuffle(list); //打乱顺序
        System.out.println(list);
        Collections.sort(list);
        System.out.println("排序" + list);
        //自定义排序，可以Student类中重写，但不会去重
        List<Student> list1 = new ArrayList<>();
        Collections.addAll(list1,new Student("小A",10,"男",10.2),
                                 new Student("小B",1,"男",10.2),
                                 new Student("小C",19,"男",10.2),
                                 new Student("小D",19,"男",10.2));
        Collections.sort(list1);
        System.out.println(list1);

        //工具类自带排序
        Collections.sort(list1, (o1,  o2)-> o2.getAge() - o1.getAge());
        System.out.println(list1);

    }
}
class Student implements Comparable<Student>{
    private String name;
    private Integer age;
    private String sex;
    private double height;

    public Student() {
    }

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

    public double getHeight() {
        return height;
    }

    public void setHeight(double height) {
        this.height = height;
    }

    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;
    }

    public String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }

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



    @Override
    public int compareTo(Student o) {
        return this.age - o.age;
    }
}