Retrieving Class Objects - Java Tutorial 5.0 英文版

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Retrieving Class Objects

You can retrieve a Class object in several ways:

• If an instance of the class is available, you can invoke Object.getClass. The getClass method is useful when you want to examine an object but you don't know its class. The following line of code gets the Class object for an object named mystery:

  Class c = mystery.getClass();
  

• If you want to retrieve the Class object for the superclass that another Class object reflects, invoke the getSuperclass method. In the following example, getSuperclass returns the Class object associated with the the TextComponent class, because TextComponent is the superclass of TextField:

  TextField t = new TextField(); 
  Class c = t.getClass(); 
  Class s = c.getSuperclass();
  

• If you know the name of the class at compile time, you can retrieve its Class object by appending .class to its name. In the next example, the Class object that represents the Button class is retrieved:

  Class c = java.awt.Button.class;
  

• If the class name is unknown at compile time, but available at runtime, you can use the forName method. In the following example, if the String named strg is set to "java.awt.Button" then forName returns the Class object associated with the Button class:

  Class c = Class.forName(strg);
  

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