How to call a static method from main in java

Question

I'm trying to implement the next code to multiply a matrix with a point or vector. But I have to use a static times method (obligatory static)

package reto3;

public class Matrix3x3 {
    public double matrix[][];

    public Matrix3x3(double matrix[][]) {
        this.matrix = matrix;
    }

    public Matrix3x3() {
        matrix = new double[3][3];
    }

    public static Point3 times(Matrix3x3 m3, Point3 p3) {
        double p[] = {p3.x, p3.y, p3.w};
        double result[] = new double[3];
        for (int i = 0; i < result.length; i++) {
            for (int j = 0; j < result.length; j++) {
                result[i] = m3.matrix[i][j] * p[j];
            }
        }
        
        return new Point3(result[0], result[1], result[2]);
    }
}

package reto3;

public class Point3 {
    
    public double point[];
    double x;
    double y;
    double w;
    
    public Point3(double x, double y, double w){
        point = new double[3];
        point[0] = x;
        point[1] = y;
        point[2] = w;
        this.x = x;
        this.y = y;
        this.w = w;
    }

    public double[] getPoint() {
        return point;
    }

    public double getX() {
        return point[0];
    }
    
    public double getY() {
        return point[1];
    }

    public double getW() {
        return point[2];
    }

    public void setX(double x) {
        point[0] = x;
    }

    public void setY(double y) {
        point[1] = y;
    }

    public void setW(double w) {
        point[2] = w;
    }
}

package reto3;

public class Main {
    public static void main(String[] args) throws Exception {
        Matrix3x3 matrix = new Matrix3x3();
        double x = 1.5;
        double y = 2.0;
        double w = 3.5;
        Point3 point3 = new Point3(x, y, w);
        Matrix3x3.times(matrix, point3);
        
    }
}

And when I compile the code it shows me the following

src/reto3/Main.java:5: error: cannot find symbol
        Matrix3x3 matrix = new Matrix3x3();
        ^
  symbol:   class Matrix3x3
  location: class Main
src/reto3/Main.java:5: error: cannot find symbol
        Matrix3x3 matrix = new Matrix3x3();
                               ^
  symbol:   class Matrix3x3
  location: class Main
src/reto3/Main.java:9: error: cannot find symbol
        Point3 point3 = new Point3(x, y, w);
        ^
  symbol:   class Point3
  location: class Main
src/reto3/Main.java:9: error: cannot find symbol
        Point3 point3 = new Point3(x, y, w);
                            ^
  symbol:   class Point3
  location: class Main
src/reto3/Main.java:10: error: cannot find symbol
        Matrix3x3.times(matrix, point3);
        ^
  symbol:   variable Matrix3x3
  location: class Main
5 errors

I'm not sure if I'm calling the method correctly or how it should be implemented with the static method.

I'd appreciate your help

The problem isn't calling a static method, it's that the compiler can't find the other classes you're trying to use inside `Main` — khelwood, Aug 28 '20 at 15:06
"And when I compile the code" how are you compiling those classes? — Federico klez Culloca, Aug 28 '20 at 15:10
What is the package structure of your project? Does `Matrix3x3` need to be imported? Is it imported? — Charlie Armstrong, Aug 28 '20 at 15:10
The package is reto3 and I compile the code wtih `javac Main.java`. — Jarvis, Aug 28 '20 at 15:14
You have to compile the others first. The correct order would be `Point3`, then `Matrix3x3`, then `Main`. Did you compile all of them? — Federico klez Culloca, Aug 28 '20 at 15:14
Ok, no, I didn't compile all of them but I already did it. And then how do I run it? — Jarvis, Aug 28 '20 at 15:19
I'm not sure if that "no" is for me, but anyway to run it, once everything is compiled, you just need `java Main` — Federico klez Culloca, Aug 28 '20 at 15:20
Having the same data in 2 places in Point3 seems unnecessary, esp. as only the array is referenced by set* and get*. Passing x, y, z separately to constructor seems a bit odd, when you could pass an array. — David G. Pickett, Aug 28 '20 at 15:20
@DavidG.Pickett to be fair the better option would be "get rid of the array", not "use an array as a parameter". `x`, `y` and `z` should be separate parameters to the constructor. — Federico klez Culloca, Aug 28 '20 at 15:22
@FedericoklezCulloca I run `java Main` and it shows this `Error: Could not find or load main class Main Caused by: java.lang.NoClassDefFoundError: reto3/Main (wrong name: Main)` — Jarvis, Aug 28 '20 at 15:26
@DavidG.Pickett I don't understand. How should I code that? :( — Jarvis, Aug 28 '20 at 15:26
@Jarvis sorry, my fault, I forgot about the package. The correct command is `java reto3.main` — Federico klez Culloca, Aug 28 '20 at 15:28
@Jarvis also see [this other question](https://stackoverflow.com/questions/11032590/how-do-i-run-a-java-class-in-a-package) for guidance. — Federico klez Culloca, Aug 28 '20 at 15:30
@FedericoklezCulloca Thank you so much! And I'm sorry, I'm new at this — Jarvis, Aug 28 '20 at 15:32

score -1 · Answer 1 · answered Aug 28 '20 at 15:17

-1

You need to import all the outside classes so they can be accessed.

So import point3 in matrix3x3 class and Import point3 and matrix3x3 in main class

Use an ide like Intellij to code.. They will take care of this automatically.

answered Aug 28 '20 at 15:17

Saurabh Nigam

795
6
12

Everything's in the same package, no need to import anything. – Federico klez Culloca Aug 28 '20 at 15:19

How to call a static method from main in java

1 Answers1