Java之反射机制四：调用类的方法

wwjj4811 2021-08-06 原文

一.调用类的公有方法

String str = "aa";
Class<? extends String> clazz = str.getClass();
Method concat = clazz.getMethod("concat", String.class);
Object bb = concat.invoke(str,"bb");
System.out.println(bb);

运行结果：

二.调用类的私有方法

1.测试类

package reflex;

public class Test {
    private String a;

    private Test(){

    }

    public Test(String a) {
        this.a = a;
    }

    public String getA() {
        return a;
    }

    public void setA(String a) {
        this.a = a;
    }

    private String concatStr(String b){
        return this.a.concat(b);
    }
}

2.调用该类的concatStr方法

@Test
    public void testInvoke() throws NoSuchMethodException, InvocationTargetException, IllegalAccessException {
        reflex.Test testStr = new reflex.Test("aa");
        Class<? extends reflex.Test> clazz = testStr.getClass();
        //获取到该私有方法的Method对象
        Method method = clazz.getDeclaredMethod("concatStr", String.class);
        //忽略访问修饰符的检查
        method.setAccessible(true);
        Object obj = method.invoke(testStr, "bb");
        System.out.println(obj);
    }

调用结果：

三.调用类的公有构造方法

@Test
    public void testConstructor() throws Exception {
        Class<reflex.Test> clazz = reflex.Test.class;
        //获取该类的Constructor对象
        Constructor<reflex.Test> constructor = clazz.getConstructor(String.class);
        //Constructor.newInstance方法可以创建该类的实例
        reflex.Test hello = constructor.newInstance("hello");
        System.out.println(hello.getA());
    }

运行结果：

四.调用类的私有构造方法

    @Test
    public void testConstructor2() throws Exception {
        Class<reflex.Test> clazz = reflex.Test.class;
        Constructor<reflex.Test> constructor = clazz.getDeclaredConstructor();
        //忽略访问修饰符的检查
        constructor.setAccessible(true);
        reflex.Test test = constructor.newInstance();
        System.out.println(test);
    }

运行结果：