java API中的单例类 [英] singleton class in java API

问题描述

Java API中的Singleton Pattern的最佳例子是什么？ Runtime类是单例吗？

What are the best examples of Singleton Pattern in Java API? Is Runtime class a singleton?

推荐答案

只有两个例子可以想到：

Only two examples comes to mind:

• java.lang.Runtime＃getRuntime（）


• java.awt.Desktop＃getDesktop（）

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

另请参阅：

• 现实世界Java API中的GoF设计模式示例

• Real world examples of GoF Design Patterns in Java API

更新：回答PeterMmm的（目前删除的）评论（问我怎么知道这是一个单例），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() {}

它每次返回相同的实例，它有一个 private 构造函数。

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

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