Singleton In JDK: java.lang.Runtime

Categories: Java; Tagged with: Java • JDK • Singleton Pattern; @ July 3rd, 2012 23:21

Some times we need write some Singleton class for some reasons, like we need a singleton to store application settings. btw, we need this singleton thread safe.

Here is a good example for open JDK:

/**
 * Every Java application has a single instance of class
 * Runtime that allows the application to interface with
 * the environment in which the application is running. The current
 * runtime can be obtained from the getRuntime method.
 * 
 * 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 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() {}

http://grepcode.com/file/repository.grepcode.com/java/root/jdk/openjdk/7-b147/java/lang/Runtime.java

The private static runtime instance will initialized when the class loaded by JVM, so thread safe is guaranteed by JVM class load mechanism.

Using Session in Servlet/JSP <-> Using Enum type in Java 在Java中使用泛型