如何根据用户输入在绘画方法中绘制墙

Question

I fairly new to programming and I have decided to take an intro to java class. I have an assignment where I have to create a wall using a for loop that changes height of the wall based on user input. I think I got most of the code right but I can't seem to connect the user input with the for loop. Any help would be appreciated.

//Package List
import java.awt.*;
import java.applet.*;
import javax.swing.*;
import java.util.*;
import java.awt.event.*;

public class Wall extends JApplet implements ActionListener{

//Component declaration
JLabel directions;
JTextField input = new JTextField( 10 );
private JButton go;
//Variable declaration
int userinput;


//Method declaration
public void init() 
{
    getContentPane().setBackground(new Color (128, 128, 128));//Changes backround of JApplet to black
    //Set JButton and JLabel
    setLayout (new FlowLayout( ));
    directions = new JLabel("Enter in any number between 1 and 20 and then press Enter on your keyboard.");
    go = new JButton( "Go!" );
    go.setBackground( Color.GREEN );
    go.setFocusPainted( false );
    go.addActionListener( this );
    add (directions );
    add (input); 
    add( go );
}

 public void actionPerformed( ActionEvent ae )
{
    String text = input.getText();
    userinput = Integer.parseInt( text );
    repaint();
}

//Method declaration 
public void paint(Graphics g) 
{
    super.paint(g);
    int startX = 50;
    int startY = 650;
    int width = 50;
    int height = 20;
    int spacing = 2;
    int xOffset = 0;
    for (int row = 0; row < userinput; row++) {
        int y = startY + (row * ( height + spacing));
        if ( row % 2 == 0) {
            xOffset = width / 2;
        } else {
            xOffset = 0;
        }
        for (int col = 0; col < 8; col++) {
            int x = xOffset + (startX + (col * (width + spacing)));
            System.out.println(x + "x" + y);
            g.setColor( Color.RED );
            g.fillRect( x, y, width, height);
        }
}
}
}

Answer 1

Basically, your code works, but your starty is to large and seems to be painting off the screen.

Generally, you should avoid overriding paint of top level containers like JApplet (why are using applets?!) and instead, use a component like JPanel instead.

A few reasons for this, but the one you will run into is that paint can paint over the child components, BUT, because of the way painting works, those child components, when updated, can paint over what you've painted ... which altogether, is just weird for the user.

Instead, separate you code into logic units, each unit should be responsible for a single unit (of logic) work

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JApplet;
import javax.swing.JButton;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextField;

public class Wall extends JApplet implements ActionListener {

//Component declaration
    JLabel directions;
    JTextField input = new JTextField(10);
    private JButton go;

    private WallPanel wallPanel;

//Method declaration
    public void init() {
        getContentPane().setBackground(new Color(128, 128, 128));//Changes backround of JApplet to black
        //Set JButton and JLabel
        setLayout(new BorderLayout());

        JPanel controls = new JPanel(new GridBagLayout());
        GridBagConstraints gbc = new GridBagConstraints();
        gbc.gridwidth = GridBagConstraints.REMAINDER;
        directions = new JLabel("Enter in any number between 1 and 20 and then press Enter on your keyboard.");
        go = new JButton("Go!");
        go.setBackground(Color.GREEN);
        go.setFocusPainted(false);
        go.addActionListener(this);
        controls.add(directions, gbc);
        controls.add(input, gbc);
        controls.add(go, gbc);

        wallPanel = new WallPanel();

        add(controls, BorderLayout.NORTH);
        add(wallPanel);
    }

    public void actionPerformed(ActionEvent ae) {
        String text = input.getText();
        wallPanel.setRowCount(Integer.parseInt(text));
        repaint();
    }

    public class WallPanel extends JPanel {

        private int rowCount;

        public void setRowCount(int rowCount) {
            this.rowCount = rowCount;
            repaint();
        }

        public int getRowCount() {
            return rowCount;
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g); 
            int startX = 50;
            int startY = 0;
            int width = 50;
            int height = 20;
            int spacing = 2;
            int xOffset = 0;
            for (int row = 0; row < getRowCount(); row++) {
                int y = startY + (row * (height + spacing));
                if (row % 2 == 0) {
                    xOffset = width / 2;
                } else {
                    xOffset = 0;
                }
                for (int col = 0; col < 8; col++) {
                    int x = xOffset + (startX + (col * (width + spacing)));
                    g.setColor(Color.RED);
                    g.fillRect(x, y, width, height);
                }
            }
        }

    }
}

So, basically, all I've done here is move the "wall painting" to it's own component/class and provided a simple setter (and getter) for changing the number of rows