请高手帮我做一下这个题？

[ghd2000]

编写一个程序，新建一个父类Addition，父类中有一个抽象方法add(),add()方法在NumberAddtion类中将两个数字相加，而在TextConcatenation类中则连接两个String(字符串)。声明属性并在父类Addition的构造方法中初始化属性。

[猿敲月下码]

应该还有更好的方法

abstract class Addition
{
	Object a,b;
	public Addition(Object a,Object b)
	{
		this.a=a;
		this.b=b;
	}
	public abstract Object add();
	
}
class NumberAddtion extends Addition
{
	public NumberAddtion(int a, int b) {
		super(a, b);
	}

	public Object add() {
		return (Integer)a+(Integer)b;
	}
}
class TextConcatenation extends Addition
{

	public TextConcatenation(String a, String b) {
		super(a, b);
	}

	public Object add() {
		return (String)a+(String)b;
	}
	
}
public class Test {
	public static void main(String[] args) {
		int a=1,b=2;
		String s="Hello ";
		String s2="World!";
		NumberAddtion n=new NumberAddtion(a,b);
		TextConcatenation t=new TextConcatenation(s,s2);
		
		System.out.println((Integer)n.add());
		System.out.println((String)t.add());
	}
		
}

[fireinjava]

顶下楼上

[Steve]

对一楼的改进一下.
1)用Java1.5的Generics简化类型转换
2)n和t不该用子类而应用父类定义子类具体化

abstract class Addition <T>
{
	T a,b;
	public Addition(T a,T b)
	{
		this.a=a;
		this.b=b;
	}
	public abstract T add();
}

class NumberAddtion extends Addition<Integer>
{
	public NumberAddtion(Integer a, Integer b) {
		super(a,b);
	}
	
	public Integer add() {
		return this.a + this.b;
	}
	
}

class TextConcatenation extends Addition<String>
{
	public TextConcatenation(String a, String b) {
		super(a,b);
	}
	
	public String add() {
		return this.a + this.b;
	}
	
}


public class Test {
	public static void main(String[] args) {
		String s1="Hello ";
		String s2="World!";
		Integer n1 = 1;
		Integer n2 = 2;
		Addition<String> addS = new TextConcatenation(s1, s2);
		Addition<Integer> addN = new NumberAddtion(n1, n2);
		System.out.println(addS.add());
		System.out.println(addN.add());
	}
		
}

[sjzxqrj]

abstract class Addition <T>
{
    T a,b;
    public Addition(T a,T b)
    {
        this.a=a;
        this.b=b;
    }
    public abstract T add();
}

class NumberAddtion extends Addition<Integer>
{
    public NumberAddtion(Integer a, Integer b) {
        super(a,b);
    }
    
    public Integer add() {
        return this.a + this.b;
    }
    
}

class TextConcatenation extends Addition<String>
{
    public TextConcatenation(String a, String b) {
        super(a,b);
    }
    
    public String add() {
        return this.a + this.b;
    }
    
}

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