isAssignableFrom

说明：

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Class中的isAssignableFrom(clazz)表示入参是否能自动转换成调用该方法的类型,入参跟类型都是Class类型。

/**

 * Created with IntelliJ IDEA.

 * User: [e-mail]

 * Date: 2014-08-17 21:25

 * Description:测试Class.assignableFrom()方法

 */

public class IsAssignableFromTest {

    public static void main(String[] args) {

        //创建对象

        A ab = new B();

        A ac = new C();

 

        B bb = new B();

        B bc = new C();

 

        C cc = new C();

 

        D dd = new D();

 

        //A.class.isAssignableFrom(..)

        System.out.println("A.class.isAssignableFrom(ab) = " + (A.class.isAssignableFrom(ab.getClass())));

        System.out.println("A.class.isAssignableFrom(ac) = " + (A.class.isAssignableFrom(ac.getClass())));

        System.out.println("A.class.isAssignableFrom(bb) = " + (A.class.isAssignableFrom(bb.getClass())));

        System.out.println("A.class.isAssignableFrom(bc) = " + (A.class.isAssignableFrom(bc.getClass())));

        System.out.println("A.class.isAssignableFrom(cc) = " + (A.class.isAssignableFrom(cc.getClass())));

        System.out.println("A.class.isAssignableFrom(dd) = " + (A.class.isAssignableFrom(dd.getClass())));

        //以下这行代码会抛出NullPointerException

        //System.out.println("A.class.isAssignableFrom(dd) = " + (A.class.isAssignableFrom(null)));

        System.out.println("-------------------------------------");

        //B.class.isAssignableFrom(..)

        System.out.println("B.class.isAssignableFrom(ab) = " + (B.class.isAssignableFrom(ab.getClass())));

        System.out.println("B.class.isAssignableFrom(ac) = " + (B.class.isAssignableFrom(ac.getClass())));

        System.out.println("B.class.isAssignableFrom(bb) = " + (B.class.isAssignableFrom(bb.getClass())));

        System.out.println("B.class.isAssignableFrom(bc) = " + (B.class.isAssignableFrom(bc.getClass())));

        System.out.println("B.class.isAssignableFrom(cc) = " + (B.class.isAssignableFrom(cc.getClass())));

        System.out.println("B.class.isAssignableFrom(dd) = " + (B.class.isAssignableFrom(dd.getClass())));

        //以下这行代码会抛出NullPointerException

        //System.out.println("B.class.isAssignableFrom(dd) = " + (B.class.isAssignableFrom(null)));

        System.out.println("-------------------------------------");

        //C.class.isAssignableFrom(..)

        System.out.println("C.class.isAssignableFrom(ab) = " + (C.class.isAssignableFrom(ab.getClass())));

        System.out.println("C.class.isAssignableFrom(ac) = " + (C.class.isAssignableFrom(ac.getClass())));

        System.out.println("C.class.isAssignableFrom(bb) = " + (C.class.isAssignableFrom(bb.getClass())));

        System.out.println("C.class.isAssignableFrom(bc) = " + (C.class.isAssignableFrom(bc.getClass())));

        System.out.println("C.class.isAssignableFrom(cc) = " + (C.class.isAssignableFrom(cc.getClass())));

        System.out.println("C.class.isAssignableFrom(dd) = " + (C.class.isAssignableFrom(dd.getClass())));

        //以下这行代码会抛出NullPointerException

        //System.out.println("C.class.isAssignableFrom(dd) = " + (C.class.isAssignableFrom(null)));

        System.out.println("-------------------------------------");

        //D.class.isAssignableFrom(..)

        System.out.println("D.class.isAssignableFrom(ab) = " + (D.class.isAssignableFrom(ab.getClass())));

        System.out.println("D.class.isAssignableFrom(ac) = " + (D.class.isAssignableFrom(ac.getClass())));

        System.out.println("D.class.isAssignableFrom(bb) = " + (D.class.isAssignableFrom(bb.getClass())));

        System.out.println("D.class.isAssignableFrom(bc) = " + (D.class.isAssignableFrom(bc.getClass())));

        System.out.println("D.class.isAssignableFrom(cc) = " + (D.class.isAssignableFrom(cc.getClass())));

        System.out.println("D.class.isAssignableFrom(dd) = " + (D.class.isAssignableFrom(dd.getClass())));

        //以下这行代码会抛出NullPointerException

        //System.out.println("D.class.isAssignableFrom(dd) = " + (D.class.isAssignableFrom(null)));

    }

}

 

对于Class的isAssignableFrom(clazz),入参是被检测的对象,A.class.isAssignableFrom(ab.getClass()),ab.getClass()为被检测对象,只要调用该方法的类型(A)

 

是被检测对象(ab.getClass())的本身类型、父类或是被检测对象实现的接口,则表达式返回true,否则返回false。