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[Notes] Collection Framework System Collection

2022-08-10 05:51:00 【hagong9】

目录

集合的理解和好处

 集合框架体系图

 Collocation基础方法

Collection遍历方式 iteration

List接口方法

集合的理解和好处

Previously to hold multiple data we used arrays,但是数组不够灵活,

 Collections have a set of methods,需要使用的时候调用即可.

 集合框架体系图

 Collocation基础方法

package com.zhang.collection_;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
@SuppressWarnings({"all"})
public class collectionDemo01 {
    public static void main(String[] args) {
        List list = new ArrayList();
        //添加单个元素
        System.out.println("=======================添加单个元素=================================");
        list.add("jack");
        list.add(100);
        list.add(true);
        list.add(18.9);
        list.add("集合");
        System.out.println("list="+list);

        //删除元素 两种方法
        System.out.println("=======================删除元素=================================");
        list.remove("jack");//删除指定元素
        System.out.println("list="+list);
        list.remove(0);//删除第一个元素
        System.out.println("list="+list);
        System.out.println("========================查找元素是否存在================================");
        //查找元素是否存在
        System.out.println(list.contains(18.9));//存在输出true
        //获取元素个数 size
        System.out.println("========================获取元素个数 size================================");
        System.out.println(list.size());
        //判断是否是空 isEmpty
        System.out.println("========================判断是否是空 isEmpty================================");
        System.out.println(list.isEmpty());
        //清空 clear
        System.out.println("========================清空 clear================================");
        list.clear();
        System.out.println("list="+list);
        //添加多个元素 addAll
        System.out.println("========================添加多个元素 addAll================================");
        ArrayList list2 = new ArrayList();
        list2.add("红楼梦");
        list2.add("三国演义");
        list.addAll(list2);
        System.out.println("list="+list);
        //查找多个元素是否都存在 containsAll
        System.out.println("========================查找多个元素是否都存在 containsAll================================");
        System.out.println(list.containsAll(list2));
        //删除多个元素 removeall()
        System.out.println("========================查找多个元素是否都存在 containsAll==========================");
        list.add("西游记");
        list.removeAll(list2);
        System.out.println("list="+list);
    }
}

 

Collection遍历方式 iteration

 Iterator usage example

package com.zhang.collection_.iteration_;

import java.awt.print.Book;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator;

public class CollectionIteration {
    public static void main(String[] args) {
        Collection col = new ArrayList();

        col.add(new Books("三国演义", "罗贯中", 160));
        col.add(new Books("红楼梦", "曹雪芹", 100));
        col.add(new Books("西游记", "吴承恩", 81));

        //System.out.println(col);
        System.out.println(col);
        //想要遍历col集合
        //1.先获得col 的迭代器
        Iterator iterator = col.iterator();
        //2.使用while循环遍历
        while (iterator.hasNext()) {
            //返回下一个元素 类型是obj
            Object obj = iterator.next();
            System.out.println(obj);

        }
        //3.当退出while循环后,这时iteration迭代器指向最后的元素
        //Traverse again if needed,需要重置迭代器.

        iterator = col.iterator();
        System.out.println("==========第二次遍历==============");
        while (iterator.hasNext()) {
            Object obj =  iterator.next();

            System.out.println(obj);
        }


    }
}
    class Books {
        private String name;
        private String author;
        private double price;

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

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

        public String getName() {
            return name;
        }

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

        public String getAuthor() {
            return author;
        }

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

        public double getPrice() {
            return price;
        }

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

集合增强for

package com.zhang.collection_;


import java.lang.reflect.Array;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;

public class iterationFor {
    public static void main(String[] args) {
        Collection col = new ArrayList();
        col.add(new Book("三国演义","罗贯中",198));
        col.add(new Book("红楼梦","曹雪芹",98));
        //使用增强for循环
        for (Object book : col) {
            System.out.println(book);
        }
        //增强forLoops can also be used with arrays
        int[] nums = {1,2,3,4};
        for (int i : nums) {
            System.out.println("i="+i);
        }
    }
}
class Book{
    private String name;
    private String author;
    private double price;


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

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

    public String getName() {
        return name;
    }

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

    public String getAuthor() {
        return author;
    }

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

    public double getPrice() {
        return price;
    }

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

List接口方法

package com.zhang.list_;

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

public class Demo01 {
    public static void main(String[] args) {
        List list = new ArrayList();
        list.add("三国演义");
        list.add("水浒传");
        list.add("西游记");
        //add (int index,object ele)在index位置插入ele元素
        list.add(1,"红楼梦");
        System.out.println(list);
        //addAll(int index,Collection eles) 从index位置开始把elesAll data is inserted
        List list2 = new ArrayList();
        list2.add("哈利波特");
        list2.add("古剑奇谭");
        list.addAll(2,list2);
        System.out.println(list);
        //get(int index)获取index位置元素
        System.out.println(list.get(2));
        //int indexOf(object obj)返回obj在集合中首次出现的位置
        System.out.println(list.indexOf("哈利波特"));
        //int lastIndexOf(object obj)返回obj在集合中末次出现的位置
        list.add(6,"哈利波特");
        System.out.println(list.lastIndexOf("哈利波特"));
        //remove（int index）移除index位置的元素
        list.remove(6);
        System.out.println(list);
        //set(int index,object obj)设置指定index位置的元素为ele,相当于替换
        list.set(2,"哈利波特与魔法石");
        System.out.println(list);
        //三种遍历方法
        Iterator iterator = list.iterator();
        while (iterator.hasNext()) {
            Object next =  iterator.next();
            System.out.println(next);
        }
        System.out.println("===================");
        for (Object o :list) {
            System.out.println(o);
        }
        System.out.println("===========================");
        for (int i =0;i<list.size();i++){
            Object obj = list.get(i);
            System.out.println(obj);
        }



    }
}

ArrayList Vector LinkList

ArrayList

 ArrayList扩容机制

 Vector

 Vector扩容

LinkList

 LinkListCreate an example of a doubly linked list

package com.zhang.list_;

import org.w3c.dom.Node;

public class LinkList_ {
    public static void main(String[] args) {
        Node node1 = new Node("小明");
        Node node2 = new Node("小红");
        Node node3 = new Node("小张");
        //双向链表连接node1 node2 node3
        node1.next = node2;
        node2.next = node3;
        node3.pre = node2;
        node2.pre = node1;

        Node frist = node1;//设置头结点
        Node last = node3;//设置尾结点
        //遍历
        while(true){
            if (frist == null){
                break;
            }else{
                System.out.println(frist);
                frist = frist.next;
            }
        }
        System.out.println("========================");
        //Add a small black between Xiaoming and Xiaohong
        Node node4 = new Node("小黑");
            node1.next = node4;
            node4.next = node2;
            node2.pre = node4;
            node4.pre = node1;
        Node frist1 = node1;//设置头结点
        Node last1 = node3;//设置尾结点
        while(true){
            if (frist1 == null){
                break;
            }else{
                System.out.println(frist1);
                frist1 = frist1.next;
            }
        }

    }

    //定义一个node类,node 对象,Represents a node in a doubly linked list.
    static class Node{
        public Object item;//存放数据
        public Node next;//指向后一个结点
        public Node pre;//指向前一个结点
        public Node(Object name){
            this.item=name;
        }
        @Override
        public String toString() {
            return "Node name="+ item;
        }


    }
}

原网站

版权声明
本文为[hagong9]所创，转载请带上原文链接，感谢
https://yzsam.com/2022/222/202208100529210675.html

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