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使用Java反射重写另一个类的方法

overriding annotations reflection class java

Nayantara Jeyaraj · 技术社区 · 7 年前

我有一个Java项目,其中有两个类。我需要使用Java反射来首先打印由中的构造函数设置的默认值 ProjectAccount.java mywork.java 类,然后我需要重写 toString() mywork.java

toString() 具有参数的方法。

package relive;

public class ProjectAccount {
    private String projectAccountID;
    private double budget;
    public int noOfProjects;

    public ProjectAccount(){
        this.projectAccountID = "MARTINDAWS-BillAnalyzer-001";
        this.budget = 120000.00;
        this.noOfProjects = 10;
    }

    @Override
    public String toString(){
        return "Project Accoutn ID = " + projectAccountID + " , Project Budget = "+budget + " , No of Projects = "+ noOfProjects;
    }
}

mywork.java

package relive;

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

public class mywork {

    public static void main(String[] args) {
        try{
            Class<?> clazz = Class.forName("relive.ProjectAccount");
            Constructor<?> constr = clazz.getDeclaredConstructor(null);
            Method mets = clazz.getDeclaredMethod("toString", null);
            Object obj = constr.newInstance(new Object[] {});

            //Print Default values
            System.out.println(mets.invoke(obj, null));

            String mod_projectAccountID="ORPT-BT-EMP-DEV";
            double mod_budget = 2200000.0;
            int mod_noOfProjects = 20;

            //Print new passed values using the overridden method
            System.out.println(mets.invoke(obj, mod_projectAccountID,mod_budget, mod_noOfProjects));        
        }

        catch(ClassNotFoundException | InstantiationException | IllegalAccessException | IllegalArgumentException | InvocationTargetException | NoSuchMethodException | SecurityException e){
            e.printStackTrace();
        }
    }
    public static String toString(String mod_projectAccountID, double mod_budget, int mod_noOfProjects){
        return "Project Accoutn ID = " + mod_projectAccountID + " , Project Budget = "+mod_budget + " , No of Projects = "+ mod_noOfProjects; 
    }

}

方法尚未确定。如有任何建议,我将不胜感激。

2 回复 | 直到 7 年前

Nayantara Jeyaraj 7 年前

我刚刚修改了 mywork.java ProjectAccount.java 直接初始化变量并进行设置。

toString() toString() 方法

package relive;

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

public class answer_a {

    public static void main(String[] args) {
        try{
            Class<?> clazz = Class.forName("relive.ProjectAccount");
            Constructor<?> constr = clazz.getDeclaredConstructor(null);
            Method mets = clazz.getDeclaredMethod("toString", null);
            Object obj = constr.newInstance(new Object[] {});

            //Print Default values
            System.out.println(mets.invoke(obj, null));

            String mod_projectAccountID= "ORPT-BT-EMP-DEV";
            double mod_budget = 2200000.0;
            int mod_noOfProjects = 20;

            //Method that accesses the Fields and modifies them with the new variables

            Field [] fields = clazz.getDeclaredFields();
            for(int y=0; y<fields.length; y++){
                fields[y].setAccessible(true);

                if(fields[y].getName() == "projectAccountID"){
                    fields[y].set(obj, mod_projectAccountID);
                }
                else if(fields[y].getType().getSimpleName() == "double"){
                    fields[y].set(obj, mod_budget);
                }
                else if (fields[y].getType().getSimpleName() == "int"){
                    fields[y].set(obj, mod_noOfProjects);
                }
            }

            System.out.println(mets.invoke(obj, null));

        }
        catch(ClassNotFoundException | InstantiationException | IllegalAccessException | IllegalArgumentException | InvocationTargetException | NoSuchMethodException | SecurityException e){
            e.printStackTrace();
        }
    }

}

-3

André 7 年前

这里有几个问题。

重写toString是通过定义实例方法(您的方法是静态的)
mets ,它引用了 ProjectAccount
mywork 不是的子类
不能添加参数,

Oracle Docs

package de.me.example;

public class SuperType {

    @Override
    public String toString() {

        return "SuperType";
    }

}


package de.me.example;

public class SubType extends SuperType {

    // this annatotion is syntactic sugar nothing more,
    //it behaves the same without it
    @Override
    public String toString() {
        return "SubType";
    }

}