Getting an error for a non static method that cant be referenced from a static context

Question

when i try to compile this it gives me an error for a non-static method begin(int) cannot be referenced from a static context. Any way this can be fixed?

import java.util.Scanner;
import objectdraw.*;
import java.awt.*;
import java.util.concurrent.TimeUnit;

public class Ricochet extends WindowController
{
    private static final int CANVAS_WIDTH=400;
    private static final int CANVAS_HEIGHT=600;

    public static void main(String [] args)
    {
        Scanner scnr = new Scanner(System.in);
        System.out.println("Enter size of box in pixels: ");
        int boxSize = scnr.nextInt();
        System.out.println("Enter number of crossings: ");
        int Crossings = scnr.nextInt();
        System.out.println("Enter pixel Speed: ");
        int pixelSpeed = scnr.nextInt();
        new Ricochet().startController(CANVAS_WIDTH, CANVAS_HEIGHT);
        begin(boxSize);

    }
    private FilledRect sq1;
    public void begin(int boxSize)
    {
        sq1 = new FilledRect(1,1, boxSize, boxSize, canvas);
        sq1.setColor(Color.GREEN);
    }
}

score 0 · Answer 1 · answered Jan 22 '15 at 12:14

0

new Ricochet().startController(CANVAS_WIDTH, CANVAS_HEIGHT); begin(boxSize);

Ricochet ricochet = new Ricochet().startController(CANVAS_WIDTH, CANVAS_HEIGHT); ricochet.begin(boxSize);

answered Jan 22 '15 at 12:14

Ivan Tamashevich

291
1
5
14

Kiki · Answer 2 · 2015-01-22T12:42:31.183

0

Instead of:

new Ricochet().startController(CANVAS_WIDTH, CANVAS_HEIGHT);
begin(boxSize);

Write:

 Ricochet ricochet = new Ricochet();
 ricochet.startController(CANVAS_WIDTH, CANVAS_HEIGHT);
 ricochet. begin(boxSize);

Your instance methods need to be called from an instance. Otherwise they need to be declared as static.

You should read this for more info:Why non-static variable cannot be referenced from a static context?

edited Jan 22 '15 at 12:42

answered Jan 22 '15 at 12:15

Kiki

2,243
5
30
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that is what i wrote in the original code :new Ricochet().startController(CANVAS_WIDTH, CANVAS_HEIGHT); begin(boxSize); – Nong Shim Jan 22 '15 at 12:37
ups :) Updated answer – Kiki Jan 22 '15 at 12:42

score 0 · Answer 3 · answered Jan 22 '15 at 12:16

You are trying to call an instance method directly from a static context. so, compiler couldn't get to an instance method without giving it an instance reference from a static context. Not possible. so, Mark the method begin as static to make it to Class level. then, it becomes accessible from static context.

Solution is

public static void begin(int boxSize)
{
    sq1 = new FilledRect(1,1, boxSize, boxSize, canvas);
    sq1.setColor(Color.GREEN);
}

The other way is to invoke the method using the instance object

Ricochet instance = new Ricochet();
instance.startController(CANVAS_WIDTH, CANVAS_HEIGHT);
instance.begin(boxSize);

Hope you understand now clearly.

i cannot make begin as a static method otherwise i will get an error for sq1 — Nong Shim, Jan 22 '15 at 12:39
Then you can make use of the second way. If you make `sq1` as also static, then also you will not get the error. — Keerthivasan, Jan 22 '15 at 12:48

Getting an error for a non static method that cant be referenced from a static context

3 Answers3