Java集合

目录

为什么需要集合

集合框架图

?Java_Collection方法

迭代器遍历（子接口也可以使用）

List接口方法

List集合排序?

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为什么需要集合

集合框架图

Java_Collection方法

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package com.edu.collection;

import com.sun.xml.internal.ws.runtime.config.TubelineFeatureReader;

import java.util.ArrayList;
import java.util.Collection;
import java.util.List;

public class Demo01 {
    public static void main(String[] args) {
        @SuppressWarnings({"all"})
        List list = new ArrayList<>();
        //add:添加元素
        list.add("jack");
        list.add(10);//相当于list.add(new Integer(10))
        list.add(true);
        System.out.println("list= "+list); //list= [jack, 10, true]

        //remove删除元素
        list.remove(0);//按索引删除第一个元素=>list= [10, true]
        System.out.println("list= "+list);
        list.remove("jack"); //按对象删除
        //查找元素是否存在 contains 返回布尔值
        System.out.println(list.contains("jack"));

        //size:获取元素个数

        //isEmpty:判读是否为空

        //clear:清空元素

        //addAll:添加多个元素
        List list2 = new ArrayList();
        list2.add(2);
        list2.add(3);
        list.addAll(list2);
        System.out.println("list= "+list);

        //containsAll 判断多个元素是否存在
        list.containsAll(list2);

        //removeAll 删除多个元素
        list.removeAll(list2);
    }
}

迭代器遍历（子接口也可以使用）

package com.edu.collection;

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

public class Demo02 {
    public static void main(String[] args) {
        Collection col = new ArrayList();
        col.add(new Book("三国演义","罗贯中",10.1));
        col.add(new Book("小李飞刀","古龙",5.1));
        col.add(new Book("红楼梦","曹雪芹",34.6));
        //遍历集合
        //1、先得到col的迭代器
        Iterator iterator = col.iterator();
        //2、使用while循环遍历
        while (iterator.hasNext()){//判断是否有数据(必需)
            Object next = iterator.next();//获取数据
            System.out.println(next);
        }

        //快捷键 itit

        //3、退出while循环后，这时iterator迭代器指向最后的元素
        //iterator.next() 会抛出异常

        //4.再次遍历,则要重置迭代器
        iterator = col.iterator();
    }
}
class Book{
    private String name;
    private String author;
    private double price;

    public Book(String name, String author, double price) {
        this.name = name;
        this.author = author;
        this.price = price;
    }


    @Override
    public String toString() {
        return "Book{" +
                "name='" + name + '\'' +
                ", author='" + author + '\'' +
                ", price=" + price +
                '}';
    }
}

List接口方法

package com.edu.list;

import java.util.ArrayList;
import java.util.List;

public class Demo01 {
    @SuppressWarnings({"all"})
    public static void main(String[] args) {
        //List集合类中的元素有序(添加顺序和取出顺序一致)、而且可以重复
        List arraysList = new ArrayList();
        arraysList.add("jack");
        arraysList.add("tom");
        arraysList.add("mary");
        arraysList.add("hasp");
        arraysList.add("jack");//可用重复
        System.out.println("list= "+arraysList);
        //2、List的每个元素都有其对应的顺序索引，即支持索引
        System.out.println(arraysList.get(2));
        /*
        常用方法
         */
        List list = new ArrayList<>();
        list.add("小张");
        list.add("小明");
        //在对应索引位置插入
        list.add(1,"小李");

        //批量加入,对应索引位置插入
        list.addAll(1,arraysList);

        //get，获取指定索引的元素
        //indexOf,获取obj在集合中首次出现的位置
        //lastIndexOf,获取最后出现的位置
        //list.remove() 可以删对象，可以删索引
        //set 指定index位置为ele，相当于替换
        list.set(2,"小非");

        //获取子集合 从索引1-2;
        List list2 = list.subList(1,3);
        System.out.println(list2);
    }
}

List集合排序?

package com.edu.list;

import java.util.ArrayList;
import java.util.List;
@SuppressWarnings({"all"})
public class Demo03 {
    public static void main(String[] args) {
        List list = new ArrayList();
        list.add(new Book("红楼梦","曹雪芹",100));
        list.add(new Book("西游记","吴承恩",10));
        list.add(new Book("水浒传","施耐庵",100));
        list.add(new Book("西游记","吴承恩",10));
        list.add(new Book("三国演义","罗贯中",20));

        for (Object o:list){
            System.out.println(o);
        }
        //对结合进行排序
        sort(list);
        System.out.println();
        for (Object o:list){
            System.out.println(o);
        }

    }
    //静态方法
    public static void sort(List list){
        int listSize = list.size();
        for (int i=0;i<listSize-1;i++){
            for (int j=0;j<listSize-1-i;j++){
                //取出对象
                Book book1 = (Book)list.get(j);
                Book book2 = (Book)list.get(j+1);
                if(book1.getPrice()>book2.getPrice()){
                    list.set(j,book2);
                    list.set(j+1,book1);
                }
            }
        }
    }
}
class Book{
    private String name;
    private int price;
    private String author;

    public Book(String name, String author,int price) {
        this.name = name;
        this.price = price;
        this.author = author;
    }

    @Override
    public String toString() {
        return "名称:"+name+"\t\t价格:"+price+"\t\t作者: "+author ;
    }

    public String getName() {
        return name;
    }

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

    public int getPrice() {
        return price;
    }

    public void setPrice(int price) {
        this.price = price;
    }

    public String getAuthor() {
        return author;
    }

    public void setAuthor(String author) {
        this.author = author;
    }
}

注意事项
ArrayList是线程不安全的，底层源码没有关键字修饰，可以加入空值?synchronized
多线程情况下，考虑使用Vector。

底层源码解析（Debug可以看见底层扩容过程！！）

LinkedList链表

package com.edu.list;

import javax.swing.plaf.synth.SynthSplitPaneUI;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;
import java.util.TooManyListenersException;

public class Demo04 {
    @SuppressWarnings({"all"})
    public static void main(String[] args) {
        //模拟简单的双向链表
        Node jack = new Node("jack");
        Node tom = new Node("tom");
        Node hsp = new Node("老汉");

        //关联
        jack.pre = null;
        jack.next = tom;
        tom.pre = jack;
        tom.next = hsp;
        hsp.pre = tom;
        hsp.next = null;

        //设置头,尾结点
        Node first = jack;
        Node last = hsp;

        //遍历
        while (true){
            if (first==null){
                break;
            }
            //输出信息
            System.out.println(first);
            first = first.next;
        }

        //插入对象
        Node smith = new Node("smith");
        smith.next = hsp;
        smith.pre = tom;
        tom.next = smith;
        hsp.pre = smith;

        first = jack;
        while (true){
            if (first==null){
                break;
            }
            //输出信息
            System.out.println(first);
            first = first.next;
        }

        List list = new LinkedList();
        list.add("jack");
        list.add("ton");
        Iterator iterator = list.iterator();
        while (iterator.hasNext()){
            Object next = iterator.next();
            System.out.println(next);
        }

        for (Object i:list){
            System.out.println(i);
        }

        for (int i=0;i<list.size();i++ ){
            System.out.println(list.get(i));
        }

    }


}
//双向链表
class Node{
    public Object item; //存数据
    public Node next;
    public Node pre;
    public Node(Object name){
        this.item = name;
    }

    @Override
    public String toString() {
        return "Node{" +
                "item=" + item +
                '}';
    }
}

?注意：LinkedList调用无参构造开辟空间为0，每次添加都是+1

Set接口基本介绍

package com.edu.set;

import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;

@SuppressWarnings({"all"})
public class Demo01 {
    public static void main(String[] args) {
        //Set常用方法
        //无重复元素，而且存取无序，可以存null，每一次运行的取出顺序相同
        //添加成功会返回一个boolean值
        Set set = new HashSet();
        set.add("jonh");
        set.add("jonh");
        set.add("lucky");
        set.add("null");
        System.out.println("set: "+set);
        System.out.println("set: "+set);

        //遍历
        //1、迭代器
        Iterator iterator = set.iterator();
        while (iterator.hasNext()){
            Object obj = iterator.next();
            System.out.println("obj:"+obj);
        }
        //2、增强for循环(本质是迭代器)
        for (Object j:set){
            System.out.println("j:"+j);
        }
        //无法使用传统for循环，无法通过索引获取

        //移除元素
        set.remove("john");

        //添加类对象,可以加进去
        set.add(new Book("A"));
        set.add(new Book("A"));
        System.out.println("set: "+set);//set: [lucky, null, Book{name='A'}, Book{name='A'}, jonh]

        //再加深 ，面试题
        set.add(new String("HASP"));//ok
        set.add(new String("HASP"));//加入不了,

    }
}
class Book{
    private String name;

    public Book(String name) {
        this.name = name;
    }

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

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