29_Collections

 

 1.概念

 

 2.常用方法

 

 3.List集合排序

 

 4.常用方法实操

package com.bfd;

import org.apache.commons.lang3.builder.HashCodeBuilder;

import java.lang.reflect.Array;
import java.util.*;

public class Demo01 {

    public static void main(String[] args) {
        ArrayList arraylist = new ArrayList();
        //1.addAll批量为collection添加元素
        Collections.addAll(arraylist, 'a', 'x', "b", 12, 199);
        System.out.println(arraylist.toString());
        //2.shuffle将list集合顺序打乱
        Collections.shuffle(arraylist);
        System.out.println(arraylist);
        //3.sort(list)将list元素按照默认规则排序(升序)
        //1.Integer
        arraylist.clear();
        Collections.addAll(arraylist, 4, 1, 10, 8, 2);
        Collections.sort(arraylist);
        System.out.println(arraylist);
        //2.Bean
        arraylist.clear();
        Collections.addAll(arraylist, new Person("k", 10), new Person("x", 12), new Person("y", 3));
        Collections.sort(arraylist);
        System.out.println(arraylist);
        //4.sort(list,Comparator匿名内部类)
        arraylist.clear();
        Collections.addAll(arraylist, "aaaaa","bb","aaa","ccc","aaa");
        Collections.sort(arraylist, new Comparator<String>() {
            @Override
            public int compare(String o1, String o2) {
                return o1.length() < o2.length() ? 1 : -1;
            }
        });
        System.out.println(arraylist);
        //Arrays和Collections中的sort的用法相同(1.使用元素自己的比较器(Comparable) 2.重新定义元素比较器Comparator)
        Person[] perarr = {new Person("k", 10), new Person("x", 12), new Person("y", 3)};
        Arrays.sort(perarr);
        System.out.println(Arrays.toString(perarr));
        Arrays.sort(perarr,new Comparator<Person>(){
            @Override
            public int compare(Person o1, Person o2) {
                return o1.age > o2.age ? 1 : -1;
            }
        });
        System.out.println(Arrays.toString(perarr));




    }
}

class Person implements Comparable<Person> {
    String name;
    int age;

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

    @Override
    public int hashCode() {
        return 1;
    }

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

    @Override
    public int compareTo(Person o) {
        return this.age > o.age ? 1 : -1;
    }
}