如何使用Java反射调用超类方法

Question

我有两节课。

public class A {

    public Object method() {...}

}

public class B extends A {

    @Override

    public Object method() {...}

}

我有一个B的实例。如何从b调用A.method（）？基本上，效果与从B调用super.method（）相同。

B b = new B();

Class<?> superclass = b.getClass().getSuperclass();

Method method = superclass.getMethod("method", ArrayUtils.EMPTY_CLASS_ARRAY);

Object value = method.invoke(obj, ArrayUtils.EMPTY_OBJECT_ARRAY);

但是上面的代码仍然会调用B.method（）

Answer 1

如果使用的是JDK7，则可以使用MethodHandle来实现：public class Test extends Base {&nbsp; public static void main(String[] args) throws Throwable {&nbsp; &nbsp; MethodHandle h1 = MethodHandles.lookup().findSpecial(Base.class, "toString",&nbsp; &nbsp; &nbsp; &nbsp; MethodType.methodType(String.class),&nbsp; &nbsp; &nbsp; &nbsp; Test.class);&nbsp; &nbsp; MethodHandle h2 = MethodHandles.lookup().findSpecial(Object.class, "toString",&nbsp; &nbsp; &nbsp; &nbsp; MethodType.methodType(String.class),&nbsp; &nbsp; &nbsp; &nbsp; Test.class);&nbsp; &nbsp; System.out.println(h1.invoke(new Test()));&nbsp; &nbsp;// outputs Base&nbsp; &nbsp; System.out.println(h2.invoke(new Test()));&nbsp; &nbsp;// outputs Base&nbsp; }&nbsp; @Override&nbsp; public String toString() {&nbsp; &nbsp; return "Test";&nbsp; }}class Base {&nbsp; @Override&nbsp; public String toString() {&nbsp; &nbsp; return "Base";&nbsp; }}

Answer 2

这是不可能的。即使使用反射，Java中的方法分派始终考虑对象的运行时类型。请参见javadoc中的Method.invoke ; 特别是本节：如果基础方法是实例方法，则使用《 Java语言规范》第二版15.12.4.4节中所述的动态方法查找来调用该方法。特别是，将发生基于目标对象的运行时类型的覆盖。

Answer 3

在@ java4script的答案的基础上，我注意到，IllegalAccessException如果您尝试从子类外部（即通常从那里super.toString()开始调用）执行此技巧，则会得到一个提示。该in方法仅在某些情况下（例如，当您从Base和一起从同一包中调用时）才绕过此方法Sub。对于一般情况，我发现的唯一解决方法是极端的（显然是不可移植的）hack：package p;public class Base {&nbsp; &nbsp; @Override public String toString() {&nbsp; &nbsp; &nbsp; &nbsp; return "Base";&nbsp; &nbsp; }}package p;public class Sub extends Base {&nbsp; &nbsp; @Override public String toString() {&nbsp; &nbsp; &nbsp; &nbsp; return "Sub";&nbsp; &nbsp; }}import p.Base;import p.Sub;import java.lang.invoke.MethodHandle;import java.lang.invoke.MethodHandles;import java.lang.invoke.MethodType;import java.lang.reflect.Field;public class Demo {&nbsp; &nbsp; public static void main(String[] args) throws Throwable {&nbsp; &nbsp; &nbsp; &nbsp; System.out.println(new Sub());&nbsp; &nbsp; &nbsp; &nbsp; Field IMPL_LOOKUP = MethodHandles.Lookup.class.getDeclaredField("IMPL_LOOKUP");&nbsp; &nbsp; &nbsp; &nbsp; IMPL_LOOKUP.setAccessible(true);&nbsp; &nbsp; &nbsp; &nbsp; MethodHandles.Lookup lkp = (MethodHandles.Lookup) IMPL_LOOKUP.get(null);&nbsp; &nbsp; &nbsp; &nbsp; MethodHandle h1 = lkp.findSpecial(Base.class, "toString", MethodType.methodType(String.class), Sub.class);&nbsp; &nbsp; &nbsp; &nbsp; System.out.println(h1.invoke(new Sub()));&nbsp; &nbsp; }}印刷SubBase