小编Nic*_*ong的帖子

当我尝试从我声明的变量创建数组时出错.

int row = 8;
int col= 8;
int [row][col];

为什么我会收到此错误:

表达式必须具有常量值.

我似乎无法理解为什么当我在quarter对象上使用println方法时,它返回toString方法的值.我从来没有调用过toString方法为什么我得到返回值？

public class Main {
    public static void main(String[] args) {
        Quarter q = new Quarter();
        Nickel n = new Nickel();
        System.out.println(q);
        System.out.println(n);
    }
}

public abstract class Money {
    private int value;

    public Money(int v) {
        value=v;
    }

    public abstract int getValue();

    protected int myValue() {
        return value;
    }

    public abstract String toString();
}

public abstract class Coin extends Money {
    public Coin(int value) {
        super(value);
        System.out.println("I am a coin, my value is " + getValue());
    }
}

public …

程序员大家好,

如果定义的变量不是在方法之外定义的公共或私有,例如:

Graphics    goff;
  Image     ii;
  Thread    thethread;

将变量定义为什么？

我正在运行一个Java类,extends Applet implements Runnable显然该程序可以运行,但没有main方法.我认为Java应用程序需要该main方法作为其入口点？

我收到一个错误:方法sleep(int)未定义Thread类型.我认为sleep方法在Java中的Thread类中.

import java.util.Random;

public class Thread implements Runnable {

    String name;
    int time;
    Random r = new Random();

    public Thread(String s){
        name = s;
        time = r.nextInt(999);
    }

    public void run() {
        try{
            System.out.printf("%s is sleeping for %d\n", name, time);
            Thread.sleep(time);
            System.out.printf("%s is done", name);
        } catch(Exception e ) {
        }
    }
}

各位程序员大家好!

JButtons应该能够出现在JFrame中吗？我在JButton上使用了setVisible方法,但它不会出现.

错误信息:

Exception in thread "main" java.lang.IllegalArgumentException: adding a window to a container
    at java.awt.Container.checkNotAWindow(Unknown Source)
    at java.awt.Container.addImpl(Unknown Source)
    at javax.swing.AbstractButton.addImpl(Unknown Source)
    at java.awt.Container.add(Unknown Source)
    at FrameTest.initializeGameFrame(FrameTest.java:27)
    at FrameTest.main(FrameTest.java:17)

码:

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;


public class FrameTest extends JFrame{

    private static final int gameWindowHeight = 700;
    private static final int gameWindowLength = 700;

    /** Set up frame for game window
     * 
     */

    public static void main(String[] args)
    {
        FrameTest.initializeGameFrame();

    }

    public static void initializeGameFrame()
    {
        FrameTest gameFrame …