There is a frame with a button and a JPanel panel. On JPanel draw shapes. This is the frame:

private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) { ((Canvas)canvas).shape = new Rect(); }

This is the Canvas code:

 import java.awt.Color; import java.awt.Graphics; import java.util.ArrayList; import java.util.logging.Level; import java.util.logging.Logger; public class Canvas extends javax.swing.JPanel { public Shape shape = null; Queue myQueue = new Queue(); public Canvas(){ super(); } @Override public void paint(Graphics g){ g.setColor(Color.white); g.fillRect(0, 0, getWidth(), getHeight()); if (shape != null) { shape.color = new Color((int)(Math.random() * 256), (int)(Math.random() * 256), (int)(Math.random() * 256)); myQueue.addShape(shape); System.out.println("shape " + shape); for (int i = myQueue.getSize; i>-1; --i){ shape = myQueue.getShape(i); shape.paint(g); } } try { shape = shape.getClass().newInstance(); } catch (InstantiationException | IllegalAccessException ex) { Logger.getLogger(Canvas.class.getName()).log(Level.SEVERE, null, ex); } repaint(); } }

Shape:

 import java.awt.Color; import java.awt.Graphics; import java.awt.MouseInfo; import java.awt.Point; public abstract class Shape { public int x1, y1, x2, y2; public Color color; public String name = "Shape"; public void paint(Graphics g){ g.setColor(color); draw(g); } public abstract void draw(Graphics g); /** * * @param evt */ public void MouseClicked(java.awt.event.MouseEvent evt) { } }

Rect:

 import java.awt.Graphics; import java.awt.MouseInfo; import java.awt.Point; import java.awt.event.MouseEvent; import javax.swing.JToggleButton; public class Rect extends Shape { @Override public void draw(Graphics g){ g.fillRect(100, 100, 100, 100); } }

Queue:

 import java.util.ArrayList; public class Queue { public ArrayList<Shape> shapes = new ArrayList<>(); public Shape nowshapes = null; int getSize; public void addShape(Shape newshapes){ shapes.add(newshapes); nowshapes = newshapes; } public Shape getShape(int i){ return shapes.get(i); } public void getSize(){ getSize = shapes.size(); } }

Actually, what is the problem: the shape class is not overridden. The figure is entered in the queue only once when you click on the button for the first time. Those. Further pressing the button leads to nothing. How to fix?

  • Let's start with the problem statement. While the presented code, when you click on the button, creates a new Rect and assigns it to the field. Then, when paint() happens, the object from the field gets a random color and is put into myQueue . Then the first object in myQueue is drawn (since getSize in for is an uninitialized class field of 0), a new Rect is created and added to canvas.shape , and the process is repeated endlessly with a call to repaint() . What is all this for? - zRrr
  • Now I realized that getSize is not initialized. What is it for? There is a queue of shapes where you can add shapes. This queue is constantly displayed during repaint (). - danilenkodanila

1 answer 1

Here is a non-optimized solution: Canvas:

 import java.awt.Color; import java.awt.Graphics; import java.util.logging.Level; import java.util.logging.Logger; public class Canvas extends javax.swing.JPanel { public Shape shape = null; Queue myQueue = new Queue(); public Canvas(){ super(); } @Override public void paint(Graphics g){ g.setColor(Color.white); g.fillRect(0, 0, getWidth(), getHeight()); System.out.println("myQueue.getSize: " + myQueue.getSize); if (shape != null) { shape.color = new Color((int)(Math.random() * 256), (int)(Math.random() * 256), (int)(Math.random() * 256)); myQueue.addShape(shape); System.out.println("shape " + shape); for (int i = myQueue.getSize-1; i>-1; --i){ //System.out.println("Я в форе и I: " + i); shape = myQueue.getShape(i); shape.paint(g); shape = null; } shape = null; } if (myQueue.getSize>0) { for (int i = myQueue.getSize-1; i>-1; --i){ //System.out.println("Я в форе и I: " + i); shape = myQueue.getShape(i); shape.paint(g); shape = null; } } repaint(); } }

Queue:

 import java.util.ArrayList; public class Queue { public ArrayList<Shape> shapes = new ArrayList<>(); public Shape nowshapes = null; int getSize = 0; public void addShape(Shape newshapes){ shapes.add(newshapes); nowshapes = newshapes; ++getSize; } public Shape getShape(int i){ return shapes.get(i); } /*public void getSize(){ getSize = shapes.size(); }*/ }