java Collection集合

一、结构

Collection
    List
        ArrayList
        LinkedList
    Set
       HashSet
       LinkedHashSet
       TreeSet

二、常用方法

1、总结

// 1.增加单个元素 
add()
// 2.增加多个元素
addAll()
// 3.删除某个元素
remove()
// 4.清空
clear()
// 5.是否为空
isEmpty()
// 6.包含某个元素
contians()
// 7.大小
size()
// 8.换成list
toArray()

2、案例

package com.wt.collection;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;

public class Demon01 {
    public static void main(String[] args) {
        Collection<String> collection = new ArrayList<>();
        // 1. add 添加单个元素
        collection.add("小明");
        collection.add("小红");
        System.out.println("collection = " + collection);
        // 2. addAll 添加多个元素
        Collection<String> collection1 = new ArrayList<>();
        collection1.add("小黑");
        collection1.add("小新");
        collection.addAll(collection1);
        System.out.println("collection = " + collection);
        // 3.remove 删
        collection1.remove("小黑");
        System.out.println("collection1 = " + collection1);
        // 4.clear 清空
        collection1.clear();;
        System.out.println("collection1 = " + collection1);
        // 5.size 获取长度
        int size = collection.size();
        System.out.println("size = " + size);
        // 6. isEmpty 判断是否为空
        boolean empty = collection1.isEmpty();
        System.out.println("empty = " + empty);
        // 7.contains 判断是否含有某个元素
        boolean contains = collection.contains("小红");
        System.out.println("contains = " + contains);
        // 8.toArray 转化成 list
        Object[] array = collection1.toArray();
        System.out.println("array = " + Arrays.toString(array));
    }
}