描述Single对象：
package android.java.oop14;
public class Single {
// 默认构造方法 私有化 不让外界调用
private Single() {}
private static final Single SINGLE = new Single();
public static Single getSingle() {
return SINGLE;
}
public void printlnData() {
System.out.println("---> 显示数据...");
}
}main测试方法：
package android.java.oop14;
public class SingleDemo {
public static void main(String[] args) {
Single single = Single.getSingle();
single.printlnData();
}
}