Collection接口的常用方法

package com.pan;

import org.junit.Test;

import java.util.*;

class Person{
    String name;
    int age;

    public Person() {
    }

    public String getName() {
        return name;
    }

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

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

    public int getAge() {
        return age;
    }

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

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

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

    @Override
    public int hashCode() {
        return Objects.hash(name, age);
    }
}

public class CollectionTest {
    @Test
    public void test1(){
        Collection coll = new ArrayList();
        //add(Object e):将元素添加到coll中
        coll.add("aa");
        coll.add("ss");
        coll.add(233);
        coll.add(new Date());
        System.out.println(coll.size());//4

        Collection coll1 = new ArrayList();
        coll1.add(456);
        coll.addAll(coll1);
        System.out.println(coll.size());//5
        System.out.println(coll);//[aa, ss, 233, Fri Aug 13 16:41:37 GMT+08:00 2021, 456]

        System.out.println(coll.isEmpty());//false
        coll.clear();
        System.out.println(coll.isEmpty());//true
    }

    @Test
    public void test2(){
        Collection coll = new ArrayList();
        coll.add(123);
        coll.add(new String("Tom"));
        coll.add(456);
        coll.add(false);
        coll.add(new Person("Jerry",10));

        //contains(Object obj):判断当前集合中是否包含obj，判断时调用obj对象所在类的equals(),如果是自定义类，那么重写equals方法
        boolean contains = coll.contains(123);
        System.out.println(contains);//true
        System.out.println(coll.contains(new String("Tom")));//true，String重写了equals()方法
        System.out.println(coll.contains(new Person("jerry",10)));
//        Person equals...
//        Person equals...
//        Person equals...
//        Person equals...
//        Person equals...
//        false
        //remove(Object obj):从当前集合中移除obj元素
        coll.remove(123);
        System.out.println(coll);//[Tom, 456, false, Person{name='Jerry', age=10}]
        System.out.println("*************************");
        coll.remove(new Person("Jerry",10));
        System.out.println(coll);
//        Person equals...
//        Person equals...
//        Person equals...
//        Person equals...
//        [Tom, 456, false]

        //removeAll(Collecction coll1):从当前集合中移除coll1中所有的元素(移除交集)
        Collection coll1 = Arrays.asList(123,456);
        coll.removeAll(coll1);
        System.out.println(coll);//[Tom, false]

    }
    @Test
    public void test3(){
        Collection coll = new ArrayList();
        coll.add(123);
        coll.add(new String("Tom"));
        coll.add(false);
        coll.add(456);
        coll.add(new Person("Jerry",10));

        //retainAll(Collection coll1):保留当前集合和coll1的交集
        Collection coll1 = Arrays.asList(123,456,789);
        coll.retainAll(coll1);
        System.out.println(coll);
//        Person equals...
//        Person equals...
//        Person equals...
//        [123, 456]

        //equals(Object obj):要想返回true，需要当前集合和形参（是一个集合）的元素都相同
        // 且如果是ArrayList还需要顺序相同

    }
    @Test
    public void test4(){
        Collection coll = new ArrayList();
        coll.add(123);
        coll.add(new String("Tom"));
        coll.add(false);
        coll.add(456);
        coll.add(new Person("Jerry",10));

        //hasCode():返回当前对象的哈希值
        System.out.println(coll.hashCode());//574407810

        //toArray():集合---》数组
        Object[] objects = coll.toArray();
        for(int i = 0; i < objects.length;i++){
            System.out.println(objects[i]);
//            123
//            Tom
//            false
//            456
//            Person{name='Jerry', age=10}

        }
        //数组---》集合:调用Arrays类的静态方法asList()
        List<String> list = Arrays.asList(new String[]{"aa","bb","cc"});
        System.out.println(list);//[aa, bb, cc]
    }
}

使用迭代器和remove删除集合中的数据

package com.pan;

import org.junit.Test;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator;

public class IteratorTest {
    //使用迭代器和remove删除集合中的数据
    @Test
    public void test1(){
        Collection coll = new ArrayList();
        coll.add(123);
        coll.add(new String("Tom"));
        coll.add(false);
        coll.add(456);
        coll.add(new Person("Jerry",10));

        Iterator iterator = coll.iterator();
        while(iterator.hasNext()){
            Object obj = iterator.next();
            if("Tom".equals(obj)){
                iterator.remove();
            }
        }
        Iterator iterator1 = coll.iterator();
        while(iterator1.hasNext()) {
            System.out.println(iterator1.next());
//            123
//            false
//            456
//            Person{name='Jerry', age=10}
        }
    }
}