使用 Reflection-with 构造函数参数在抽象类中创建一个实例

Question

Create an instance within Abstract Class using Reflection 我之前打开了类似的问题。但是现在我通过添加带有 int 参数的构造函数来更改派生类。现在我有并且“没有这样的方法异常”。这是源代码和异常。

public abstract class Base {

    public Base(){
        this(1);
    }

    public Base(int i){
        super();
    }

    public Base createInstance() throws Exception{
        Class<?> c = this.getClass();       
        Constructor<?> ctor = c.getConstructor();
        return ((Base) ctor.newInstance());     
    }

    public abstract int  getValue();

    }


    public class Derived extends Base{

    public Derived(int i) {
        super(2);
    }

    @Override
    public int getValue() {
        return 10;
    }


    public static void main(String[] args) {
        try {
            Base b1=new Derived(2);
            Base b2 =b1.createInstance();

            System.out.println(b2.getValue());

        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

}

它抛出这个堆栈跟踪

java.lang.NoSuchMethodException: reflection.Derived.<init>()
    at java.lang.Class.getConstructor0(Unknown Source)
    at java.lang.Class.getConstructor(Unknown Source)
    at reflection.Base.createInstance(Base.java:17)
    at reflection.Derived.main(Derived.java:18)

Answer 1

请尝试

import java.lang.reflect.Constructor;

public abstract class Base {

    public Base() {
        this(1);
    }

    public Base(int i) {
        super();
    }

    public Base createInstance() throws Exception {
        Class<?> c = this.getClass();
        Constructor<?> ctor = c.getConstructor(new Class[] { int.class });
        return ((Base) ctor.newInstance(new Object[] { 1 }));
    }

    public abstract int getValue();

}

Answer 2

正如异常明确指出的那样，问题是reflection.Derived.<init>() 不存在。这是因为您的 Derived 类没有任何默认构造函数。

你需要使用：

Class<?> c = this.getClass();
Constructor<?> ctor = c.getConstructor(Integer.class);
ctor.newInstance(intValue);