JAVA基础（002_forEach的实现原理）

来源：互联网发布：浪潮服务器安装centos 编辑：程序博客网时间：2024/06/07 16:56

forEach的实现原理

核心：forEach遍历的实现是对迭代器的使用。在API中，对Iterable<T>接口有这样的描述，实现此接口，允许对象成为”for-each loop”语法的target。

public interface Iterable<T>

Implementing this interface allows an object to be the target of the “for-each loop” statement.

以List集合为例：List<E>接口继承了Collection<E>接口，而Collection<E>接口继承了Iterable<E>接口。Iterable<E>接口中定义了迭代器。

public interface Collection<E> extends Iterable<E>
public interface List<E> extends Collection<E>

API源码如下（JDK8）：public interface Iterable<T> {    Iterator<T> iterator();    default void forEach(Consumer<? super T> action) {        Objects.requireNonNull(action);        for (T t : this) {            action.accept(t);        }    }    default Spliterator<T> spliterator() {    return Spliterators.spliteratorUnknownSize(iterator(), 0);    }}

forEach遍历示例：

public class MainClass {    public class User {        private String username;        private String password;        public String getUsername() {            return username;        }        public void setUsername(String username) {            this.username = username;        }        public String getPassword() {            return password;        }        public void setPassword(String password) {            this.password = password;        }    }    public static void main(String[] args) {        // 添加测试数据        List<User> users = new ArrayList<User>();        for (int i = 0; i < 5; i++) {            User user = new MainClass().new User();            user.setUsername("张三" + i);            user.setPassword("00000" + i);            users.add(user);        }        // forEach遍历        for (User user : users) {            System.out.println("username: " + user.getUsername() + "," + " " + "password: " + user.getPassword());        }    }}

官方文档：
http://docs.oracle.com/javase/8/docs/api/index.html
http://docs.oracle.com/javase/8/docs/technotes/guides/language/foreach.html

0 0