如何将 ImageIcon 设置为 JLabel 数组？

Question

我已经创建了一个将 ImageIcon 添加到下一个空 JLabel 的程序，编译器没有显示错误，为什么这不起作用？ setEmptySpace 包含一个返回空白空间的循环，并且 getCar 方法应该设置图标。

package CarPark;
//add imports
import java.awt.Color;
import java.awt.GridLayout;
import javax.swing.BorderFactory;
import javax.swing.ImageIcon;
import javax.swing.JLabel;
import javax.swing.JPanel;

public class Park extends JPanel
{

    //declare a JLabel array for parking space
    JLabel[] parkingSpace;
    //declare ImageIcon class for cars
    ImageIcon car;

    public Park()
    {
        //create a new instance of the parking space array with 12 spaces
        parkingSpace = new JLabel[12];
        //populate array
        for (int i = 0; i < parkingSpace.length; i++)
        {
            //create parking space JLabels
            //parkingSpace[i] = new JLabel(String.valueOf(i + 1));
            parkingSpace[i] = new JLabel();
            //set parking space colour
            parkingSpace[i].setBackground(new Color(85, 55, 170));
            //make JLabels opaque
            parkingSpace[i].setOpaque(true);

        }

        //create grid for parking space setting rows, columns, horizontal gap and vertical gap
        this.setLayout(new GridLayout(4, 3, 4, 4));
        //set background colour to white
        this.setBackground(new Color(255, 255, 255));

        //add 12 parking spaces to panel
        for (int i = 0; i < 12; i++)
        {
            this.add(parkingSpace[i]);
            //create a red border with a thickness of 4 pixels
            parkingSpace[i].setBorder(BorderFactory.createLineBorder(Color.RED, 4));
        }
    }
    //find an empty parking space
    int setEmptySpace()
    {
        for(int i = 0; i < parkingSpace.length; i++)
        {
            if(parkingSpace[i] == null)
            {
                return i;
            }
        }
        return -1;
    }
    //add car image to empty parking space
    void getCar(int getEmptySpace)
    {
         car = new ImageIcon("car.png");

         parkingSpace[getEmptySpace].setIcon(car);
    }
}

Answer 1

基于您的构造函数...

for (int i = 0; i < parkingSpace.length; i++) {
    //create parking space JLabels
    //parkingSpace[i] = new JLabel(String.valueOf(i + 1));
    parkingSpace[i] = new JLabel();
    //set parking space colour
    parkingSpace[i].setBackground(new Color(85, 55, 170));
    //make JLabels opaque
    parkingSpace[i].setOpaque(true);
}

这是不可能的……

int setEmptySpace() {
    for (int i = 0; i < parkingSpace.length; i++) {
        if (parkingSpace[i] == null) {
            return i;
        }
    }
    return -1;
}

返回除-1 以外的任何内容，因为每个parkingSpace 都包含一个JLabel

我认为您想要做的是检查JLabel 的icon 属性是否为null，例如

int setEmptySpace() {
    for (int i = 0; i < parkingSpace.length; i++) {
        if (parkingSpace[i].getIcon() == null) {
            return i;
        }
    }
    return -1;
}

Answer 2

我尝试将我的代码简化为更多的方法，每个方法只做一件事，而不是尝试每个方法执行多个任务。我想知道的是 setCarIconToLabel() 是否实际上将图标设置为 JLabel，如果没有，它怎么能被改变。这种方法也是正确的类型，因为我认为它不应该是无效的，但我不知道还能设置什么？

//find an empty parking space and return it's number
int emptySpaceNo()
{

    for(int i = 0; i < parkingSpace.length; i++)
    {
        System.out.println("Test method 1 Park P 1");
        if(parkingSpace[i].getIcon() == null)
        {
            System.out.println("Test method 1 P 2");
            return i;

        }
    }
    return -1;
}

//return JLabel that is null
JLabel findEmptySpace()
{
    return parkingSpace[emptySpaceNo()];
}

//create new car image icon
ImageIcon setCarIcon()
{
    ImageIcon carIcon = new ImageIcon("car.png");

    return carIcon;
}

//set car icon to JLabel parking space
void setCarIconToLabel()
{
  findEmptySpace().setIcon(setCarIcon());
}