Java.java example

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/**
 * Alipay.com Inc.
 * Copyright (c) 2004-2012 All Rights Reserved.
 */
package com.alipay.zdal.datasource.resource.util.platform;

import com.alipay.zdal.datasource.resource.util.ThrowableHandler;

/**
 * Provides common access to specifics about the version of <em>Java</em>
 * that a virtual machine supports.
 *
 * <p>Determines the version of the <em>Java Virtual Machine</em> by checking
 *    for the availablity of version specific classes.<p>
 *
 * <p>Classes are loaded in the following order:
 *    <ol>
 *    <li><tt>java.lang.Enum</tt> was introduced in JDK 1.5</li>
 *    <li><tt>java.lang.StackTraceElement</tt> was introduced in JDK 1.4</li>
 *    <li><tt>java.lang.StrictMath</tt> was introduced in JDK 1.3</li>
 *    <li><tt>java.lang.ThreadLocal</tt> was introduced in JDK 1.2</li>
 *    <li><tt>java.lang.Void</tt> was introduced in JDK 1.1</li>
 *    </ol>
 * </p>
 *
 * @author ����
 * @version $Id: Java.java, v 0.1 2014-1-6 ����05:43:14 Exp $
 */
public final class Java {
    /** Prevent instantiation */
    private Java() {
    }

    /** Java version 1.0 token */
    public static final int  VERSION_1_0 = 0x01;

    /** Java version 1.1 token */
    public static final int  VERSION_1_1 = 0x02;

    /** Java version 1.2 token */
    public static final int  VERSION_1_2 = 0x03;

    /** Java version 1.3 token */
    public static final int  VERSION_1_3 = 0x04;

    /** Java version 1.4 token */
    public static final int  VERSION_1_4 = 0x05;

    /** Java version 1.5 token */
    public static final int  VERSION_1_5 = 0x06;

    /** 
     * Private to avoid over optimization by the compiler.
     *
     * @see #getVersion()   Use this method to access this final value.
     */
    private static final int VERSION;

    /** Initialize VERSION. */
    static {
        // default to 1.0
        int version = VERSION_1_0;

        try {
            // check for 1.1
            Class.forName("java.lang.Void");
            version = VERSION_1_1;

            // check for 1.2
            Class.forName("java.lang.ThreadLocal");
            version = VERSION_1_2;

            // check for 1.3
            Class.forName("java.lang.StrictMath");
            version = VERSION_1_3;

            // check for 1.4
            Class.forName("java.lang.StackTraceElement");
            version = VERSION_1_4;

            // check for 1.5
            Class.forName("java.lang.Enum");
            version = VERSION_1_5;
        } catch (ClassNotFoundException e) {
            ThrowableHandler.add(e);
        }
        VERSION = version;
    }

    /**
     * Return the version of <em>Java</em> supported by the VM.
     *
     * @return  The version of <em>Java</em> supported by the VM.
     */
    public static int getVersion() {
        return VERSION;
    }

    /**
     * Returns true if the given version identifer is equal to the
     * version identifier of the current virtuial machine.
     *
     * @param version    The version identifier to check for.
     * @return           True if the current virtual machine is the same version.
     */
    public static boolean isVersion(final int version) {
        return VERSION == version;
    }

    /**
     * Returns true if the current virtual machine is compatible with
     * the given version identifer.
     *
     * @param version    The version identifier to check compatibility of.
     * @return           True if the current virtual machine is compatible.
     */
    public static boolean isCompatible(final int version) {
        // if our vm is the same or newer then we are compatible
        return VERSION >= version;
    }
}