Question

Java正在给我这个错误。我已经工作了一段时间，我很难过。我无法弄清楚为什么java找不到总和？提前致谢。：

C:\Users\Keegan\Documents\TwoNumbers.java:70: error: cannot find symbol

System.out.println( sum );
                            ^
symbol:   variable sum

location: class TwoNumbers

1 error

以下是代码：

public class TwoNumbers {

    /*** Class Constants ***/

    private final double DEFAULT_NUMBER1 = 10;
    private final double DEFAULT_NUMBER2 = 15;

    /*** Class Variables -- State of the object ***/

    private double number1;
    private double number2;

    /*** Constructor Methods -- Set the state of the object  double n1, double n2***/

    public TwoNumbers () {

         number1 = DEFAULT_NUMBER1;
         number2 = DEFAULT_NUMBER2;
    }

    public void setNumbers ( double n1, double n2 ) {

        this.number1=n1;

        this.number2=n2;
    }

    /*** Accessor methods ***/

    public double getNumber1() {

        return number1;
    }

    public double getNumber2() {

        return number2;

    }

    public double sum(double n1, double n2) {

        double sum;

        sum = n1 + n2;

        return sum;
    }


    /*** Transformer/Mutator Methods ***/

    public static void main( String args[] ) {

        System.out.println( sum );
        System.out.println("" );
        System.out.println("" );
        System.out.println("" );
        System.out.println("" );
        System.out.println("" );
        System.out.println("" );
    }

}

Answer 1

sum被定义为sum方法中的局部变量，它没有此方法的上下文（或无法访问）......

public double sum(double n1, double n2) {
    double sum;

根据您的代码尝试执行的操作，您不应该尝试以任何方式访问它，而应该只是使用TwoNumbers的实例来打印结果...

System.out.println(new TwoNumbers().sum(1, 1));

例如......

Answer 2

因为变量sum的范围仅在您声明它的方法中可见。

您无法访问仅对您未调用的方法本地的变量。

public double sum(double n1, double n2) {
    double sum;
    sum = n1 + n2;
    return sum;
} // sum is no longer visible to anything else
// the variable was used and garbage collected within the sum() method.

Answer 3

变量“sum”被定义为方法“sum”中的局部变量。在发生错误的“main（）”函数中，唯一可见的名称“sum”是成员函数。要调用它，您需要创建一个实例，并使用带有这样的参数的括号：

public static void main(String args[]) {
    TwoNumbers instance = new TwoNumbers();
    System.out.println(instance.sum(1, 2));  // prints 3
    System.out.println("" );
    System.out.println("" );
    System.out.println("" );
    System.out.println("" );
    System.out.println("" );
    System.out.println("" );
}

为什么Java找不到我的符号？

3 个答案: