Java 返回NullPointerException的数组

我一直在创建一个Snakes程序，其中包含一个

段数组

。在这种情况下，我认为使用数组作为顺序至关重要。第一个问题是，即使在我创建了一个“new

Segment

实例”之后，它也不会显示任何正方形（这是蛇的第一段）。但是，当我将

System.out.println（）

语句放在paint方法（稍后显示）中时，它抛出一个

NullPointerException

。代码如下：

注意：方法

increaseSegmentCount（）

从外部类调用过一次。而且，这不是完整的代码

蛇

将

System.out.println

语句放入后的

paint（）

方法：

@Override
    public void paint(Graphics g) {
        for (Segment segment : segments) {
            if (segment != null)
                System.out.println("Called")
                segment.paint(g);
        }
    }

段

类（非常简单的类）

View

类中的

paintComponent（）

方法（用于调试）

最后是错误（在插入print语句之后…在插入之前没有错误）：

---

有什么想法吗？另外，请不要将此标记为重复，并将我指向另一个显示如何解决NPE问题的帖子。。。我已经知道该做什么和正在发生什么（大部分情况下），但这是我遇到的一件奇怪的事情，非常令人困惑。谢谢。

当您添加打印语句时，您需要{}作为您的if

if (segment != null) {
            System.out.println("Called")
            segment.paint(g);
}

---

您可以考虑使用自动代码格式化程序，这将使缩进明显。

您在添加打印语句时需要{}……< /p>

if (segment != null) {
            System.out.println("Called")
            segment.paint(g);
}

您可以考虑使用自动代码格式化程序，这将使缩进明显。

@Override
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        for (Entity entity : model.getEntities()) {
            entity.paint(g);
        }
    }

Called
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at Snake.paint(Snake.java:61)
    at View.paintComponent(View.java:50)
    at javax.swing.JComponent.paint(Unknown Source)
    at javax.swing.JComponent.paintToOffscreen(Unknown Source)
    at javax.swing.RepaintManager$PaintManager.paintDoubleBuffered(Unknown Source)
    at javax.swing.RepaintManager$PaintManager.paint(Unknown Source)
    at javax.swing.RepaintManager.paint(Unknown Source)
    at javax.swing.JComponent._paintImmediately(Unknown Source)
    at javax.swing.JComponent.paintImmediately(Unknown Source)
    at javax.swing.RepaintManager$4.run(Unknown Source)
    at javax.swing.RepaintManager$4.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
    at javax.swing.RepaintManager.paintDirtyRegions(Unknown Source)
    at javax.swing.RepaintManager.paintDirtyRegions(Unknown Source)
    at javax.swing.RepaintManager.prePaintDirtyRegions(Unknown Source)
    at javax.swing.RepaintManager.access$1200(Unknown Source)
    at javax.swing.RepaintManager$ProcessingRunnable.run(Unknown Source)
    at java.awt.event.InvocationEvent.dispatch(Unknown Source)
    at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
    at java.awt.EventQueue.access$500(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
    at java.awt.EventQueue.dispatchEvent(Unknown Source)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.run(Unknown Source)

if (segment != null) {
            System.out.println("Called")
            segment.paint(g);
}