java - 引用 JTabbedPane 的属性时出现 NullPointerException

Question

创建 JTabbedPane 和获取选项卡计数背后的逻辑有什么问题11，然后使用 setter？

我尝试引用 SetObjects.currentJTabbedPane 的 tabCount 并抛出异常NullPointerException。

创建

jtp.setSelectedIndex(0);

int jtpCount=jtp.getTabCount();
System.out.println(C+M+AND+jtpCount+": jtpCount of The JTabbedPane created: \n");

setCurrentJTabbedPane(jtp);
int currentCount=SetObjects.currentJTabbedPane.getTabCount();
System.out.println(C+M+AND+currentCount+": currentCount for
    SetObjects.currentJTabbedPane.getTabCount() : \n");

二传手

public static void setCurrentJTabbedPane(JTabbedPane currentJTabbedPane) {
    String M =(" --> in setCurrentJTabbedPane() var: <-- \n");
    System.out.println(M);

    SetObjects.currentJTabbedPane = currentJTabbedPane;
    System.out.println(C+M+AND+SetObjects.currentJTabbedPane.getTabCount()+":
        SetObjects.currentJTabbedPane.getTabCount() : \n");
}

输出

CLASS
SetObjects:
--> JTabbedPane obj() var: xxxxxxxxx : xxxxxxxx<--
: 11: jtpCount of The JTabbedPane created:

--> in setCurrentJTabbedPane() var: <-- 

Exception in thread "main" java.lang.NullPointerException
at view.SetObjects.setCurrentJTabbedPane(SetObjects.java:385)
at view.SetObjects.obj(SetObjects.java:217)
at view.SchoolJDesktopPane.createInnerFrame(SchoolJDesktopPane.java:119)
at view.SchoolJDesktopPane.(SchoolJDesktopPane.java:97)
at view.Main.createJDesktopPane(Main.java:60)
at view.Main.main(Main.java:54)

Answer 1

你路过吗null至setCurrentJTabbedPane ？尝试添加更多 System.out.println 语句来检查可能出现问题的每个变量。另外，让你的调试语句更简单，即替换 System.out.println(A + B + C)具有三种不同的陈述。

编辑:拆分调试语句的原因是 if System.out.println(object1.foo() + ", " + object2.bar())抛出 NullPointerException 那么你不知道哪个对象为 null。将其分成两个语句意味着堆栈跟踪可以准确地告诉您问题出在哪里。