java接口..。快速提问

Question

你能告诉我这条线是怎么工作的吗..。我的OperatorFactory.get("add")没有做任何事情。我不会把任何东西印出来

ArithmeticOperator add = OperatorFactory.get ("add");

当我有以下情况时：

interface ArithmeticOperator {

    // Returns the result of applying the operator to operands a and b.
    double operate (double a, double b);

    // Return a String that is the name of this operator.
    String printName ();
}


public class OperatorFactory implements ArithmeticOperator {



    public OperatorFactory(){

    }

    public static ArithmeticOperator get(String name){
        if(name.equals("add"))
                return new PlusOperator();
        else if(name.equals("sub"))
                return new SubOperator();
        else if(name.equals("mult"))
                return new MultOperator();
        else if(name.equals("div"))
                return new DivOperator();
        else
            return null;
    }

    public double operate(double a, double b) {
        throw new UnsupportedOperationException("Not supported yet.");
    }

    public String printName() {
        throw new UnsupportedOperationException("Not supported yet.");
    }

}

public class PlusOperator extends OperatorFactory {



    public double operate(double a, double b) {
        return a + b;

    }

    public String printName() {
        return "Add";
    }

}




public class PlusOperator extends OperatorFactory {



    public double operate(double a, double b) {
        return a + b;

    }

    public String printName() {
        return "Add";
    }

}

Answer 1

您从不调用add.printName()，当然也不会输出任何内容，所以我并不奇怪什么都没有打印出来。

Answer 2

你真的试过打印名字吗？

ArithmeticOperator add = OperatorFactory.get ("add");
System.out.println(add.printName());

另外，PlusOperator应该直接实现ArithmeticOperator。工厂不应该实现ArithmeticOperator。这允许您从工厂类中移除操作和printName方法。

Answer 3

不像get()方法调用printName()，因此不应该打印任何内容。