Why does DrJava return a Static Error?

问题:

I use dr java for linux to run my code. I've been running into a bunch of errors recently while running this simple program. The code compiles fine but whenever I run the java file, I get the error; Static Error: Undefined name here's my code; (I've got two files, Square.java and SquareD.java) Here's Square.java

public class Square{
    private String name;
    private int y;
    private int x;

    public Square(String st,int x2,int y2){
        name=st;
        x=x2;
        y=y2;
    }

    public int square(){
        return x*x+y*y;
    }

    double a1=(double) x;
    double a2=(double) y;

    public double hypotenuse(double a1,double a2){
        double sum = a1*a1+a2*a2;
        return Math.sqrt(sum);
    }

    public int area(){
        return x*y;
    }

    public String getName(){
        return name;
    }
}

Here's SquareD.java;

public class Square{
    private String name;
    private int y;
    private int x;

    public Square(String st,int x2,int y2){
        name=st;
        x=x2;
        y=y2;
    }

    public int square(){
        return x*x+y*y;
    }

    double a1=(double) x;
    double a2=(double) y;

    public double hypotenuse(double a1,double a2){
        double sum = a1*a1+a2*a2;
        return Math.sqrt(sum);
    }

    public int area(){
        return x*y;
    }

    public String getName(){
        return name;
    }
}

Whever I type java Square.java or java SquareD.java in the interactions window, I get,

Static Error: Undefined name

I'm running Ubuntu 11.10

回答1:

You don't run a class by typing java Square.java, but java Square.

^{(Or run Square, the equivalent of hitting the Run button.)}

But you'll still need a main method with the following signature:

public static void main(String[] args) {
    // etc.
}

Then when you type java Square (assuming you've compiled it) it will run whatever is in main.