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Runtime源码

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 Runtime are instance     * methods and must be invoked with respect to the current runtime object.     *     * @return  the Runtime object associated with the current     *          Java application.     */    public static Runtime getRuntime() {
           return currentRuntime;    }    /** Don't let anyone else instantiate this class */    private Runtime() {
   }}

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分析

• 先看构造：

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

构造设为private，无法调用new对象。

• 在看如何获取对象：

用 public static 的方法$getRuntime()$，可以通过静态调用获得对象。

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

• 最后，看单例的来源：

private static Runtime currentRuntime = new Runtime();

在类初始化时候new一次对象，用$currentRuntime$引用。

饿汉式 or 懒汉式

上述方法为“饿汉式”，即在类初始化时候就 new 出唯一的对象。

public class Runtime {
       private static Runtime currentRuntime = null;    /**     * Returns the runtime object associated with the current Java application.     * Most of the methods of class Runtime are instance     * methods and must be invoked with respect to the current runtime object.     *     * @return  the Runtime object associated with the current     *          Java application.     */    public static Runtime getRuntime() {
       	if(currentRuntime == null){
       		currentRuntime = new Runtime();    	}        return currentRuntime;    }    /** Don't let anyone else instantiate this class */    private Runtime() {
   }}

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