java - 调用 method.getReturnType().newInstance()(静态内部类的静态方法)时出现 InstantiationException

Question

我明白

run: method: foo
Return type: class java.lang.Integer
Exception in thread "main" java.lang.InstantiationException: java.lang.Integer
  at java.lang.Class.newInstance0(Class.java:359)
  at java.lang.Class.newInstance(Class.java:327)
  at newinstancetest.NewInstanceTest.main(NewInstanceTest.java:10)
Java Result: 1 BUILD SUCCESSFUL (total time: 0 seconds)

当我运行这个时: 打包新实例测试； 导入java.lang.reflect.Method;

public class NewInstanceTest {

public static void main(String[] args) throws NoSuchMethodException, InstantiationException, IllegalAccessException {
    Method method = InnerClass.class.getDeclaredMethod("foo", null);
    System.out.println("method: " + method.getName());
    System.out.println("Return type: " + method.getReturnType());
    Object obj = method.getReturnType().newInstance();
    System.out.println("obj: " + obj);
}

public static class InnerClass {
    public static Integer foo() {
        return new Integer(1);
    }
}
}

“obj”+ obj 不应该打印对新对象的引用吗？知道为什么我会得到异常吗？

Answer 1

该方法的返回类型是Integer，它没有no-arg构造函数。要复制 foo 方法中的实例，您可以这样做

Object obj = method.getReturnType().getConstructor(int.class).newInstance(1);