Java API中的单例类示例 | API中的单例类示例

本文介绍了Java API中的单例类示例的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！

问题描述

Java API中Singleton设计模式的最佳示例是什么？ Runtime 类是单例吗？

What are the best examples of the Singleton design pattern in the Java APIs? Is the Runtime class a singleton?

推荐答案

只有两个例子注意：

java.lang.Runtime#getRuntime()
java.awt.Desktop#getDesktop()

请参见也：

Real world examples of GoF Design Patterns in Java API

更新：要回答PeterMmm（当前已删除？）的评论（问我如何知道这是一个单例），请检查javadoc和源代码：

Update: to answer PeterMmm's (currently deleted?) comment (which asked how I knew that it was a singleton), check the javadoc and source code:

public class Runtime {
    private static Runtime currentRuntime = new Runtime();

    /**
     * Returns the runtime object associated with the current Java application.
     * Most of the methods of class <code>Runtime</code> are instance
     * methods and must be invoked with respect to the current runtime object.
     *
     * @return  the <code>Runtime</code> object associated with the current
     *          Java application.
     */
    public static Runtime getRuntime() {
        return currentRuntime;
    }

    /** Don't let anyone else instantiate this class */
    private Runtime() {}

每次都返回相同的实例，并且具有 private 构造函数。

It returns the same instance everytime and it has a private constructor.

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