求助,求大神指出错误啊！ - JAVA论坛

问题点数：0 回复次数：2

求助,求大神指出错误啊！

package 实验;

abstract class Bred {
    String name;

    public void speakName() {
        System.out.println("这是一只 " + this.name);
    }

    public void math() {
    };

    public String toString() {
        return name;
    }
}

class FengHuang extends Bred {
    final String name = "凤凰";

    public void math() {
        System.out.println("他会做算术");
    }
}

class Psittaciformes extends Bred {
    final String name = "鹦鹉";

    public void math() {
        System.out.println("他会做算术");
    }
}

class MaQue extends Bred {
    final String name = "麻雀";

    public void math() {
        System.out.println("他不会做算术");
    }
}

class Work {

    public static Bred getAdd(String name) throws Exception {
        Bred aa = null;
        try {
            if ("凤凰".equals(name)) {
                aa = new FengHuang();
            }
            if ("鹦鹉".equals(name)) {
                aa = new Psittaciformes();
            }
            if ("麻雀".equals(name)) {
                aa = new MaQue();
            }
        } catch (Exception e) {
            System.out.println(e);
        }
        return aa;
    }
}

public class WorkGround {
    public static void main(String[] args) {
        // Bred a=null;
        try {
            Work w = new Work();
            w.getAdd("凤凰").speakName();
        } catch (Exception e) {
            System.out.println(e);
        }
    }
}
结果是这是一只 null
我希望是  这是一只凤凰

[ 本帖最后由 long8863 于 2013-3-5 19:30 编辑 ]

搜索更多相关主题的帖子: public　package　abstract　凤凰　 void　

第 2 楼

得分:0

程序代码：

abstract class Bred {
    String name;

    public void speakName() {
        System.out.println("这是一只 " + this.name);
    }

    public void math() {
    };

    public String toString() {
        return name;
    }
}

class FengHuang extends Bred {
   

    public FengHuang(){
        name="凤凰";
    }

    public void math() {
        System.out.println("他会做算术");
    }
}

class Psittaciformes extends Bred {
    public Psittaciformes(){
        name="鹦鹉凰";
    }

    public void math() {
        System.out.println("他会做算术");
    }
}

class MaQue extends Bred {
    public MaQue(){
        name="麻雀";
    }
    public void math() {
        System.out.println("他不会做算术");
    }
}

class Work {

    public static Bred getAdd(String name) throws Exception {
        Bred aa = null;
        try {
            if ("凤凰".equals(name)) {
                aa = new FengHuang();
            }
            if ("鹦鹉".equals(name)) {
                aa = new Psittaciformes();
            }
            if ("麻雀".equals(name)) {
                aa = new MaQue();
            }
        } catch (Exception e) {
            System.out.println(e);
        }
        return aa;
    }
}

public class WorkGround {
    public static void main(String[] args) {
        // Bred a=null;
        try {
            Work w = new Work();
            w.getAdd("凤凰").speakName();
        } catch (Exception e) {
            System.out.println(e);
        }
    }
}

speakName方法是子类继承父类的，方法中this.name是指父类中的name
但是你在每个子类中又重新定义了name属性，复制时是对子类中的name赋值，所以父类中的name是null
我把你每个子类中的name定义都删掉了，子类会继承父类的name属性，直接在构造函数中赋值初始化即可

[ 本帖最后由 shellingford 于 2013-3-5 23:05 编辑 ]

第 3 楼

得分:0

下面代码能实现你的功能，你的结果之所以是这是一只null是因为你的程序是实现继承，从基类开始调用的，以下代码能实现你要的……
package 实验；
abstract class Bred {
    String name;

    public void speakName() {
        System.out.println("这是一只 " + name);
    }

    public void math() {
    };

    public String toString() {
        return name;
    }
}

class FengHuang extends Bred {
    final String name = "凤凰";
    public void speakName() {
        System.out.println("这是一只 " + name);
    }
    public void math() {
        System.out.println("他会做算术");
    }
}

class Psittaciformes extends Bred {
    final String name = "鹦鹉";
    public void speakName() {
        System.out.println("这是一只 " + name);
    }
    public void math() {
        System.out.println("他会做算术");
    }
}

class MaQue extends Bred {
    final String name = "麻雀";
    public void speakName() {
        System.out.println("这是一只 " + name);
    }
    public void math() {
        System.out.println("他不会做算术");
    }
}

class Work {

    public static Bred getAdd(String name) throws Exception {
        Bred aa = null;
        try {
            if ("凤凰".equals(name)) {
                aa = new FengHuang();
            }
            if ("鹦鹉".equals(name)) {
                aa = new Psittaciformes();
            }
            if ("麻雀".equals(name)) {
                aa = new MaQue();
            }
        } catch (Exception e) {
            System.out.println(e);
        }
        return aa;
    }
}

public class Test {
    public static void main(String[] args) {
        try {
            Work w = new Work();
            w.getAdd("凤凰").speakName();
        } catch (Exception e) {
            System.out.println(e);
        }
    }
}