java - 反射不起作用

Question

我是反射(reflection)新手。我面临一些错误。请帮忙。下面是我的代码:

EmployeeClass.java:

public class EmployeeClass {

    private String empID;
    private String empName;

    public String getEmpID() {
        return empID;
    }

    public void setEmpID(String empID) {
        this.empID = empID;
    }

    public String getEmpName() {
        return empName;
    }

    public void setEmpName(String empName) {
        this.empName = empName;
    }

    public EmployeeClass(String empID, String empName) { 
        this.empID = empID;
        this.empName = empName;
    }

    public String getAllDetails() {
        return empID + " " + empName;
    }

}

ReflectionClass.java:

import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

public class ReflectionClass {

    public static void main(String[] args) {

        EmployeeClass emp = new EmployeeClass("1", "Emp1");
        Method method = null;
        try {
            method = emp.getClass().getMethod("getAllDetails", null);
            System.out.println(method.invoke(null, null));
        } catch (NoSuchMethodException | SecurityException
                | IllegalAccessException | IllegalArgumentException
                | InvocationTargetException e) {
            System.out.println(e.getMessage());
        }


    }

}

运行 ReflectionClass.java 时，出现以下错误:

线程“main”中的异常 java.lang.NullPointerException

at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
                at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
                at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
                at java.lang.reflect.Method.invoke(Unknown Source)
                at myprgs.programs.ReflectionClass.main(ReflectionClass.java:14)

Answer 1

调用invoke()时，您需要传递类的对象(包含您的方法)，如下所示:

method.invoke(emp, null);

更改:

System.out.println(method.invoke(null, null));

致:

System.out.println(method.invoke(emp, null));