Class 及instanceof关键字的应用

class Base{
	public void draw(){
		System.out.println("Base");
	}
}
class Driver extends Base{
	public void draw(){
		System.out.println("Driver");
	}
}
public class TestClass {
	
	public static void test(Object x){
		System.out.println(x.getClass());
		
		System.out.println("x instanceof Base " + (x instanceof Base));
		System.out.println("x instanceof Driver " + (x instanceof Driver));
		System.out.println("Base.class.isInstance(x) " + Base.class.isInstance(x));
		System.out.println("Driver.class.isInstance(x) " + Driver.class.isInstance(x));
		System.out.println("x.getClass() == Base.class " + (x.getClass() == Base.class));
		System.out.println("x.getClass() == Driver.class " + (x.getClass() == Driver.class));
		System.out.println("x.getClass().equals(Base.class)) " + (x.getClass().equals(Base.class)));
		System.out.println("x.getClass().equals(Driver.class)) " + (x.getClass().equals(Driver.class)));
		//instanceof 与 isInstance的结果是一样的。
	}
	public static void main(String[] args) {
		try {	
			//创建该类的Class对象
			Class cls = Driver.class;
			Class cls1 = Class.forName("Driver");
			((Driver)cls.newInstance()).draw();
			((Driver)cls1.newInstance()).draw();
		} catch (ClassNotFoundException e) {
			e.printStackTrace();
		} catch (InstantiationException e) {
			e.printStackTrace();
		} catch (IllegalAccessException e) {
			e.printStackTrace();
		}
		
		test(new Base());
		System.out.println("---------------------------------------------------");
		test(new Driver());
	}
}

 

运行结果：

Driver
Driver
class com.lwf.exception.Base
x instanceof Base true
x instanceof Driver false
Base.class.isInstance(x) true
Driver.class.isInstance(x) false
x.getClass() == Base.class true
x.getClass() == Driver.class false
x.getClass().equals(Base.class)) true
x.getClass().equals(Driver.class)) false
---------------------------------------------------
class com.lwf.exception.Driver
x instanceof Base true
x instanceof Driver true
Base.class.isInstance(x) true
Driver.class.isInstance(x) true
x.getClass() == Base.class false
x.getClass() == Driver.class true
x.getClass().equals(Base.class)) false
x.getClass().equals(Driver.class)) true

 

Class用于描述一切类，它的实例就是类在JVM中的一份字节码。Class提供了泛型以明确使用的是具体哪一个类的字节码。

得到Class实例的三种方式：

1、类名.class如  Class c = Date.class;

2、Class.forName方法如 Class c = Class.forName("com.lwf.test.TestDate");

3、调用对象的getClass方法，该方法继承自Object类。如 Class c = new ArrayList().getClass(); 返回的是运行时的对象的字节码。

 基本数据类型及void都可使用.class返回。如int.class ; void.class等。

 基本数据类型包装类的TYPE属性返回基本类型的字节码：Integer.class != int.class，Integer.TYPE= int.class