请问java中Exception in thread "main"这种报错是什么意思?
Exception in thread "main" java.lang.NullPointerException
at java.awt.Container.addImpl(Unknown Source)
at java.awt.Container.add(Unknown Source)
at 实验八.Calculator.<init>(Calculator.java:44)
at 实验八.Calculator.main(Calculator.java:143)
附我的部分代码:
private String[] KEYS = { "0", "1", "2", "3", "4", "5", "6","7", "8", "9"};
private JButton jbtNum[] = new JButton[KEYS.length];
p1.add(jbtNum[7]);
这种写法有问题吗?