Iterator(迭代器)

Iterator介绍

1、Iterator对象称为迭代器，主要用于遍历 Collection 集合中的元素

2、所有实现了Collection 接口的集合类都有一个iterator()方法，用以返回一个实现了Iterator接口的对象，即可以返回一个迭代器

3、Iterator 仅用于遍历集合，其本身并不存放对象。

Iterator运行原理

Iterator接口的方法

while循环

package com.zhang;

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

public class Iterator_ {
    public static void main(String[] args) {
        ArrayList arrayList = new ArrayList();
        arrayList.add(new Book("三国演义", "罗贯中", 10.1));
        arrayList.add(new Book("红楼梦", "曹雪芹", 132.1));
        arrayList.add(new Book("小李飞刀", "古龙", 23.43));
        System.out.println(arrayList);

        Iterator iterator = arrayList.iterator();
        while (iterator.hasNext()) {
            Object next =  iterator.next();
            System.out.println(next);
        }
        // 此时迭代器的指针已经到了最后一个元素，如果再运行Iterator.next()将会报错
//        iterator.next(); // NoSuchElementException

        // 重置迭代器指针的方法为：
        iterator = arrayList.iterator();
        System.out.println("-------------- 重置指针后，继续遍历 -------------- ");
        while (iterator.hasNext()) {
            Object next =  iterator.next();
            System.out.println(next);
        }
    }
}

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;
    }

    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;
    }

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

for循环增强

简述：

增强for循环，可以替代迭代器，

特点：增强for循环其实是简单的Iterator。本质上是一样的，只能用于遍历数组和集合

基本语法:

package com.zhang;

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

public class Iterator_ {
    public static void main(String[] args) {
        ArrayList arrayList = new ArrayList();
        arrayList.add(new Book("三国演义", "罗贯中", 10.1));
        arrayList.add(new Book("红楼梦", "曹雪芹", 132.1));
        arrayList.add(new Book("小李飞刀", "古龙", 23.43));
        System.out.println(arrayList);
        
        // for循环增强
        for (Object o :
                arrayList) {
            System.out.println(o);
        }
    }
}

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;
    }

    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;
    }

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