JDK 源码解读之 Number类

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public abstract class Number implements java.io.Serializable {

　　Number类有修饰符 abstract 。表明Number类定义了一些方法，并没有具体实现，需要子类自己实现，关于abstract ，quaro上一个答案写的很清晰：

　　　　The “abstract” Keyword

1. The keyword abstract can be used on classe declaration. For example abstract MyClassX (…);.
2. The keyword abstract can be used on method declaration. For example abstract int f (…);.
3. When a class is declared abstract, it cannot be instantiated.
4. When a method is declared abstract, it cannot have definition.
5. Only abstract classes can have abstract methods. Abstract class does not necessarily require its methods to be all abstract.

JDK 源码解读之 Number类

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原文地址：http://www.cnblogs.com/goodearth/p/7240001.html