迭代器模式

刺骨的言语ヽ痛彻心扉 2022-05-30 08:22 302阅读 0赞

### [迭代器模式][Link 1] ###

> Provides a way to access the elements of an aggregate object without exposing its underlying represenation.

迭代器模式可以用以访问聚合对象中各个元素, 而又无须暴露该对象的内部表示。  
![这里写图片描述][70]

### 代码示例 ###

> Iterator接口，泛型接口

public interface Iterator<T> {
        boolean hasNext();
    
        T next();
    }

> 容器，泛型接口

public interface Container<T> {
        Iterator<T> iterator();
    }

> 具体容器，泛型类，这样我们可以存储遍历多种类型数据，比如在下面的代码中，我们存储了整型和类对象

public class SimpleContainer<T> implements Container<T> { 
        public T[] names;
        private int size = 0;
    
        public SimpleContainer(int length) {
            names = (T[]) new Object[length];
        }
    
        public void add(T t) {
            if (size < names.length) {
                names[size++] = t;
            }
        }
    
        @Override
        public Iterator iterator() {
            return new SimpleIterator();
        }
    
        private class SimpleIterator<T> implements Iterator<T> { 
            int index;
    
            @Override
            public boolean hasNext() {
                if (index < names.length) {
                    return true;
                }
                return false;
            }
    
            @Override
            public T next() {
                if (this.hasNext()) {
                    return (T) names[index++];
                }
                return null;
            }
        }
    }

> 测试多种类型的数据遍历

public class Main {
    
        public static void main(String[] args) {
            SimpleContainer<String> names = new SimpleContainer(8);
            for (int i = 0; i < 8; i++) {
                names.add(String.valueOf(i));
            }
            for (Iterator iterator = names.iterator(); iterator.hasNext(); ) {
                System.out.println("Name : " + iterator.next());
            }
    
            SimpleContainer<User> users = new SimpleContainer<>(8);
            for (int i = 0; i < 8; i++) {
                users.add(User.builder().id(i).name("user" + i).build());
            }
            for (Iterator iterator = users.iterator(); iterator.hasNext(); ) {
                System.out.println(iterator.next());
            }
        }
    }

> User类定义，建造者模式

public class User {
        private int id;
        private String name;
    
        private User(int id, String name) {
            this.id = id;
            this.name = name;
        }
    
        @Override
        public String toString() {
            return String.format("id is %s, name is %s", id, name);
        }
    
        public static Builder builder() {
            return new Builder();
        }
    
        static class Builder {
            private int id;
            private String name;
    
            public Builder id(int id) {
                this.id = id;
                return this;
            }
    
            public Builder name(String name) {
                this.name = name;
                return this;
            }
    
            public User build() {
                return new User(id, name);
            }
        }
    }

[Link 1]: https://github.com/ypmc/design-pattern
[70]: /images/20220530/4d97b01010124b2abf09fd4969f75cfb.png