java - Java API 中单例类的示例

Question

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

Answer 1

只有两个例子浮现在脑海中:

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

另见:

• Real world examples of GoF Design Patterns in Java API

---

更新:回答 PeterMmm(目前已删除？)的评论(询问我如何知道它是单例)，检查 javadoc 和源代码:

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() {}

它每次都返回相同的实例，并且它有一个private 构造函数。