3、形式: public class Singleton { private static Singleton instance = null; public static synchronized Singleton getInstance() { //这个方法比上面有所改进,不用每次都进行生成对象,只是第一次 //使用时生成实例,提高了效率! if (instance==null) instance=new Singleton();return instance; } } 其他形式:定义一个类,它的构造函数为private的,所有
4、方法为static的。一般认为第一种形式要更加安全些 136、继承时候类的执行顺序问题,一般都是选择题,问你将会打印出什么?答:父类:package test;public class FatherClass{ public FatherClass() { System.out.println("FatherClass Create"); }}子类:package test;import test.FatherClass;public class ChildClass extends FatherClass{ public ChildClass()
5、{ System.out.println("ChildClass Create"); } public static void main(String[] args) { FatherClass fc = new FatherClass(); ChildClass cc = new ChildClass(); }}输出结果:C:>java test.ChildClassFatherClass CreateFatherClass CreateChildClass Create 137、内部类的实现方式?答:示例代码如下:package test;publ
6、ic class OuterClass{ private class InterClass { public InterClass() { System.out.println("InterClass Create"); } } public OuterClass() { InterClass ic = new InterClass(); System.out.println("OuterClass Create"); } public static void main(String[] args) { OuterClass oc = new
7、 OuterClass(); }}输出结果:C:>java test/OuterClassInterClass CreateOuterClass Create再一个例题:public class OuterClass { private double d1 = 1.0; //insert code here } You need to insert an inner class declaration at line 3. Which two inner class declarations are valid?(Choose two.) A. c