禮悟：
好好學習多思考，尊師重道存感恩。葉見尋根三返一，活水清源藏於零。
虛懷若谷良心主，皓月當空自在王。願給最苦行無悔，誠勸且行且珍惜。

os ：windows7 x64
jdk：jdk-8u131-windows-x64
ide：Eclipse Oxygen Release (4.7.0)

源碼(僅提取出能顯示出單例模式-餓漢式 特征性的代碼)：

/*
 * Copyright (c) 1995, 2013, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

package java.lang;

import java.io.*;
import java.util.StringTokenizer;
import sun.reflect.CallerSensitive;
import sun.reflect.Reflection;

/**
 * Every Java application has a single instance of class
 * <code>Runtime</code> that allows the application to interface with
 * the environment in which the application is running. The current
 * runtime can be obtained from the <code>getRuntime</code> method.
 * <p>
 * An application cannot create its own instance of this class.
 *
 * @author  unascribed
 * @see     java.lang.Runtime#getRuntime()
 * @since   JDK1.0
 */

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() {}

源碼分析：

API：

Java優秀，值得學習。
設計模式中蘊含著極高的智慧，對項目開發有大幫助。
學習資源：itcast和itheima視頻庫。如果您有公開的資源，可以分享給我的話，用您的資源學習也可以。
博文是觀看視頻後，融入思考寫成的。博文好，是老師講得好。博文壞，是 給最苦 沒認真。

Java基礎 Runtime 用了單例模式中的餓漢式