Question

这段代码有什么问题。在eclipse中为什么显示该方法必须返回一个double值？

public void setLength(double length){
    if(length>0.0 && length<20.00){
        this.length=length;
    }else{
        dataRight=false;
        throw new IllegalArgumentException( "Length is not correct." );
    }
}

public double  getLength(){
    if(dataRight==false){
        System.out.printf("\nAs wrong data, calculation Not possible.\n ");
    }else{
        return length;
    }
}

Answer 1

因为您在此处定义了double类型的结果值：

public double  getLength()
      {
        if(dataRight==false)
        {
         System.out.printf("\nAs wrong data, calculation Not possible.\n ");
        }
        else
        {
          return length;
        }
       }

但是在你的第一个if condition中你什么也没有回复。

至少返回第一个condition的默认值，如果绝对无效则抛出exception。

if(dataRight==false)
        {
         System.out.printf("\nAs wrong data, calculation Not possible.\n ");
         return -1;
        }

或

public double  getLength() throws Exception
  {
    if(dataRight==false)
    {
     System.out.printf("\nAs wrong data, calculation Not possible.\n ");
     throw new Exception("wrong data, calculation Not possible.");
    }
    else
    {
      return length;
    }
   }

Answer 2

if(dataRight==false)
    {
     System.out.printf("\nAs wrong data, calculation Not possible.\n ");
    // should return from here as well or throw exception 
    }

Answer 3

错误发生在getLenght（）方法中。

如果if语句中的条件为true，则不返回任何内容。否则，你返回一个双倍。

因此Java编译器（而不是Eclipse）期望返回一个double。

你可能想要像

这样的东西

public double getLength() {
    if( dataRight == false )
        throw new RuntimeException("\nAs wrong data, calculation Not possible.\n ");
    return this.length;
}

Answer 4

 public double  getLength()
 {
    if(dataRight==false)
    {
       System.out.printf("\nAs wrong data, calculation Not possible.\n ");
       return 0.0; //<-- Return path must exist for all possible paths in a method, you could also add exception handling
    }
    else
       return length;
 }

Answer 5

public class Test {

    private double length;
    private boolean dataRight = true;

    public void setLength(double length) {
        if (length > 0.0 && length < 20.00) {
            this.length = length;
        } else {
            dataRight = false;
            throw new IllegalArgumentException("Length is not correct.");
        }
    }

    public double getLength() {
        if (!dataRight) {
            System.out.printf("\nAs wrong data, calculation Not possible.\n ");
            return 0.0; // <<<--- If dataRight is false then return double
                        // default values
        }
        return length;
    }

    public static void main(String[] args) {
        Test test= new Test();
        test.setLength(24);
        System.out.println(test.getLength());
    }
}

方法在Java中返回值

5 个答案: