Repaint Method in Java

[eabod]

Hello,

Why in the code below is the repaint method constantly called? I only want repaint to be called when the "Go" button is pushed.



import java.awt.*;
import java.applet.Applet;
import java.awt.Graphics;
import java.awt.event.*;
import java.io.BufferedReader;
import java.io.*;
import java.net.URL;
import java.net.*;
import javax.swing.Box;
import javax.swing.BoxLayout;


public class Assignment3 extends Applet implements ActionListener {

String url;
TextField inputLine = new TextField("Enter URL here.",15);
TextArea console = new TextArea("", 6,80, TextArea.SCROLLBARS_VERTICAL_ONLY );
Button pushButton = new Button("Go");

public void paint (Graphics g) {
String currentLine;
URL target;
int line = 1;
int j, B=0;
int[] kArray={}, wArray={}, x={};
try {
target = new URL(url);
BufferedReader dis = new BufferedReader(new InputStreamReader(target.openStream()));
while (((currentLine = dis.readLine()) != null) && line <= 3) {
if (line == 1) {
B = Integer.parseInt(currentLine);
}
else if (line == 2) {
String[] strk = currentLine.split("\t");
kArray = new int[strk.length];
for ( j = 0; j < strk.length;j++) {
kArray[j] = Integer.parseInt(strk[j]);
}
}
else if (line == 3) {
String[] strw = currentLine.split("\t");
wArray = new int[strw.length];
for ( j = 0; j < strw.length;j++) {
wArray[j] = Integer.parseInt(strw[j]);
}
}
line++;
}
x= WtCoins(B, kArray, wArray);
for (j = 0; j < x.length; j++) {
console.append(Integer.toString(x[j])+"\t");
}
console.append("\n");
}
catch (Exception e) {
if (url.equals(null) != true) {
console.append("Error message: " + e.toString() + "\n");
}
}
}

public Assignment3() {
setLayout(new BoxLayout(this, BoxLayout.Y_AXIS));
add(Box.createVerticalStrut(100));
add(console);
add(inputLine);
add(pushButton);
pushButton.addActionListener(this);
console.setEditable(false);
}


public void init() {
resize(500, 250);
}
public void actionPerformed(ActionEvent event) {
url = inputLine.getText();
repaint();
}

public int[] WtCoins(int B, int[] k, int[] w) {
int[][] x = new int[B+1][k.length];
int[] F = new int[B+1];
int i, j, min, minIndex=0, s;
for (j = 1; j <= B; j++) {
min = -1;
for (i = 0; i < k.length; i++) {
if (k[i] <= j && F[j-k[i]] != -1) {
if (min == -1 || (w[i] + F[j-k[i]])< min) {
min = w[i] + F[j-k[i]];
minIndex = i;
}
}
}
F[j] = min;
if (min != -1) {
for (s = 0; s < k.length; s++) {
x[j][s] = x[j-k[minIndex]][s];
}
x[j][minIndex]++;
}
}
return x[B];
}
}


Thanks.

[TennTux]

I believe your problem may be the way the "paint" method works not the fact that you call "repaint" method in "actionPerformed".

I believe the key to understanding this is that "paint" is called every time the applet needs to be redrawn/displayed. And, this can happen for many reasons. e.g. The user minimizes the browser then restores it on the screen; Another window is displayed in front of the applet (does not require the whole applet to be obstructed only partial. This could even be your development environment/debugger). "paint" may be called once or a thousand times depending on what else is happening around your program and you have little control over when paint is controled.

Hope this helps.