“线程中的异常”;“主要”;适用于初学者的java.lang.NullPointerException
我知道这已经被告知很多次了,但我已经用java编程3周了,我只是在做一些有趣的东西。人们所做的其他大多数报告都没有解决我的问题。屏幕显示但不显示rect。这是我的密码:“线程中的异常”;“主要”;适用于初学者的java.lang.NullPointerException,java,Java,我知道这已经被告知很多次了,但我已经用java编程3周了,我只是在做一些有趣的东西。人们所做的其他大多数报告都没有解决我的问题。屏幕显示但不显示rect。这是我的密码: import java.awt.Rectangle; import javax.swing.JFrame; import java.awt.Color; public class something { public static int SCREEN_WIDTH = 500; public static in
import java.awt.Rectangle;
import javax.swing.JFrame;
import java.awt.Color;
public class something {
public static int SCREEN_WIDTH = 500;
public static int SCREEN_HEIGHT = 500;
public static int Y = 10;
public static int X = 10;
public static int Width = 50;
public static int Height = 50;
public static Color player_color = Color.black;
public static Graphics g;
public static void screen() {
JFrame screen = new JFrame();
screen.setVisible(true);
screen.setSize(SCREEN_WIDTH, SCREEN_HEIGHT);
screen.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
screen.setTitle("test");
screen.setResizable(false);
}
public static void player() {
Rectangle r = new Rectangle(Y, X, Width, Height);
g.fillRect((int)r.getX(), (int)r.getY(), (int)r.getWidth(), (int)r.getHeight());
g.setColor(player_color);
}
public static void main(String[] args) {
screen();
player();
}
}
顺便说一下,我正在使用Eclipse,我想问题是我正在使用一个空值的值?如果我错了,请纠正我。您的g为null且未初始化为任何值,因此您在访问fillRect()方法时将获得null指针 您只需在类级别使用extends Applet并重写paint method()
g
为null
。不要让所有的都是静态的
。因为图形类是一个抽象基类,不能直接实例化。实例通常由组件创建,并作为组件的update()和paint()方法的参数传递给程序。我认为您需要先创建画布,然后才能在其中绘制矩形Canvas c=新画布();g=c.getGraphics()```
public class something extends Applet {
public static int SCREEN_WIDTH = 500;
public static int SCREEN_HEIGHT = 500;
public static int Y = 10;
public static int X = 10;
public static int Width = 50;
public static int Height = 50;
public static Color player_color = Color.black;
@Override
public void paint(Graphics g) {
JFrame screen = new JFrame();
screen.setVisible(true);
screen.setSize(SCREEN_WIDTH, SCREEN_HEIGHT);
screen.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
screen.setTitle("test");
screen.setResizable(false);
Rectangle r = new Rectangle(Y, X, Width, Height);
g.fillRect((int) r.getX(), (int) r.getY(), (int) r.getWidth(), (int) r.getHeight());
g.setColor(player_color);
}