Question

我将borderX1-Y2的变量放在顶部，但我没有将它们分配给paint方法。我检查了方法中的值并且它们是正确的，但是当我用另一种方法检查它们时它们是0.如何让它们保持它们的值？

public void paint(Graphics g)
{       
    borderX1 = 20;
    borderY1 = 20;
    borderX2 = getWidth();
    borderY2 = getHeight();

    g.setColor(Color.white);
    g.fillRect(0, 0, borderX2, borderY2);
    g.setColor(Color.blue);
    g.drawRect(borderX1, borderY1, borderX2 - 40, borderY2 - 40);
}

继承其他一切（我削减了不必要的位）

public class ShapePanel extends JPanel
{
private int borderX1;
private int borderY1;
private int borderX2;
private int borderY2;

public ShapePanel(){}

public void paint(Graphics g)
{
    borderX1 = 20;  
    borderY1 = 20;
    borderX2 = getWidth();
    borderY2 = getHeight();

    g.setColor(Color.white);
    g.fillRect(0, 0, borderX2, borderY2);
    g.setColor(Color.blue);
    g.drawRect(borderX1, borderY1, borderX2 - 40, borderY2 - 40);
}

public int getX1()
    {return borderX1;}

public int getY1()
    {return borderY1;}

public int getX2()
    {return borderX2;}

public int getY2()
    {return borderY2;}
}

我的错误在于我的返回，它们为所有这些返回值为0

我可以初始化像这样的变量

private int borderX1 = 20;
private int borderY1 = 20;
private int borderX2 = 762;
private int borderY2 = 533;

但我想要根据窗口大小

更改X2和Y2的值

Answer 1

在调用值之前，需要先初始化值。您可以先拨打paint(Graphics g)或全局初始化该值。

Answer 2

您正在使用不同的对象调用paint和其他方法。请确保两者是同一个对象。如果您调用paint方法，然后使用相同的对象调用另一个方法，则将保留这些值。

class Sample{
    int borderX1,borderY1,borderX2 ,borderY2 ;

    public void paint(Graphics g)
    {
       borderX1 = 20;
       borderY1 = 20;
       borderX2 = getWidth();
       borderY2 = getHeight();
     }
     public void fun1(Graphics g){

     }
 }

 Sample s1 = new Sample(); 
 s1.paint(Graphics)     borderX1 =20,borderY1=20,borderX2=some width ,borderY2 =some height
 Sample s2 = new Sample();
 s2.fun1();//borderX1=0,borderY1=0,borderX2=0 ,borderY2=0 these values should be 0

Java实例字段值仅在方法中更改

2 个答案: