Collection学习第三天

喜欢ヅ旅行 2022-09-03 14:12 244阅读 0赞

今天主要学习了iterator迭代循环

学习了next方法和hasNext方法以及对迭代器的重置

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQ1MDMwOTY2_size_16_color_FFFFFF_t_70][]

迭代器的执行原理

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQ1MDMwOTY2_size_16_color_FFFFFF_t_70 1][]

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQ1MDMwOTY2_size_16_color_FFFFFF_t_70 2][]

下面展示代码：

package com.company;
    
    import java.util.ArrayList;
    import java.util.Iterator;
    
    public class IteratorMethod {
        public static void main(String[] args) {
            ArrayList list = new ArrayList();
    
            list.add(new Book("三毛记", "马龙", 15.8));
            list.add(new Book("二毛记", "许昕", 18.8));
            list.add(new Book("一毛记", "张继科", 16.8));
            Iterator iterator = list.iterator();
    
    //        使用hasNext方法检查下一个元素是否存在
            while(iterator.hasNext()){
    //            Object object = iterator.next();
    //            System.out.println(object);
    //            使用iterator.next()遍历下一个元素
                System.out.println(iterator.next());
            }
    //        System.out.println(iterator.next());
            System.out.println("第二次输出");
    
    //        当退出循环时，此时的iterator指向最后一个元素
    //        当我们还需要遍历时，就必须重置迭代器，使用 iterator = list.iterator();
                iterator = list.iterator();
            while (iterator.hasNext()){
                System.out.println(iterator.next());
            }
    
    
    
    
        }
    }
    class Book{
    
    
        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;
        }
    
        public Book(String name, String author, double price) {
            this.name = name;
            this.author = author;
            this.price = price;
        }
    
        private String name;
        private String author;
        private double price;
    
        @Override
        public String toString() {
            return "Book{" +
                    "name='" + name + '\'' +
                    ", author='" + author + '\'' +
                    ", price=" + price +
                    '}';
        }
    }

结果：

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQ1MDMwOTY2_size_16_color_FFFFFF_t_70 3][]

增强for循环，底层仍然是使用了迭代器，可以说是一个简化版的迭代器

源码如图：

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQ1MDMwOTY2_size_16_color_FFFFFF_t_70 4][]

调用了hasNext方法![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQ1MDMwOTY2_size_16_color_FFFFFF_t_70 5][]

调用了next方法

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQ1MDMwOTY2_size_16_color_FFFFFF_t_70 6][]

代码：

for(Object object:list){
                System.out.println("obj="+object);
            }

结果：

![20210808090750900.png][]

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQ1MDMwOTY2_size_16_color_FFFFFF_t_70 7][]

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQ1MDMwOTY2_size_16_color_FFFFFF_t_70]: /images/20220829/871b5620d3124ea8820eff1790ada82b.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQ1MDMwOTY2_size_16_color_FFFFFF_t_70 1]: /images/20220829/c5d5c03d4254446db11deaf840adeae2.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQ1MDMwOTY2_size_16_color_FFFFFF_t_70 2]: /images/20220829/32525585eaa14d45bcdd42777dc2508f.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQ1MDMwOTY2_size_16_color_FFFFFF_t_70 3]: /images/20220829/0060706527f64b7faa2644588cfd1f93.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQ1MDMwOTY2_size_16_color_FFFFFF_t_70 4]: /images/20220829/1cfba5e282824bb28b28baaed883846d.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQ1MDMwOTY2_size_16_color_FFFFFF_t_70 5]: /images/20220829/6f81e8c3e4e7409b9148c8ed4967b184.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQ1MDMwOTY2_size_16_color_FFFFFF_t_70 6]: /images/20220829/70a280ce96b54f6a8c0cdbc641d7c552.png
[20210808090750900.png]: /images/20220829/4688159173994fccab498b2b2546abb3.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQ1MDMwOTY2_size_16_color_FFFFFF_t_70 7]: /images/20220829/7a32c68a6f5a4d96938abbaea70159fa.png