一个正确的单例

public class A{
    public final static A instance = new A();
    public static A getA(){
        return instance;
    }
   //something to do
}

package com.liangyumingblog;

public class SimpleSinglton
{
    private static class Instance
    {
        private final static SimpleSinglton instance = new SimpleSinglton();
    }

    public SimpleSinglton getInstance()
    {
        return Instance.instance;
    }
}