在JPanel中獲取NullPointerException jPanel = jDayChooser1.getDayPanel（）

Question

在此我試圖從mysql數據庫中獲取日期，並通過設置color.But在JPanel jPanel = jDayChooser1.getDayPanel()中顯示這​​些日期，即時獲取錯誤'NullPointerException'。

public Calender() { 

// retrieving the dates from db 

    getDates c = new getDates(); 
    Date[] a = c.Dates(); 

    Calendar cal = Calendar.getInstance(); 
    int day = cal.get(Calendar.DAY_OF_MONTH); 
    int month = cal.get(Calendar.MONTH); 
    int year = cal.get(Calendar.YEAR); 

    JPanel jPanel = jDayChooser1.getDayPanel(); 

    Component component[] = jPanel.getComponents(); 

    for(int i=0;i<a.length;i++) { 
     if(month == a[i].getMonth() && year == a[i].getYear()) { 
     component[ a[i].getDay()].setBackground(Color.blue); 
     } 
    } 

    initComponents(); 
} 

這裏的堆棧跟蹤...

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException at greetingcard.Calender.<init>(Calender.java:37) at greetingcard.Calender$1.run(Calender.java:100) at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:251) at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:721) at java.awt.EventQueue.access$200(EventQueue.java:103) at java.awt.EventQueue$3.run(EventQueue.java:682) at java.awt.EventQueue$3.run(EventQueue.java:680) at java.security.AccessController.doPrivileged(Native Method) at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76) at java.awt.EventQueue.dispatchEvent(EventQueue.java:691) at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:242) at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:161) at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:150) at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:146) at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:138) at java.awt.EventDispatchThread.run(EventDispatchThread.java:91) BUILD SUCCESSFUL (total time: 5 seconds)

Answer 1

想通出來.. :)

public Calender() { 
initComponents(); 

// retrieving the dates from db 

getDates c = new getDates(); 
Date[] a = c.Dates(); 

Calendar cal = Calendar.getInstance(); 
int day = cal.get(Calendar.DAY_OF_MONTH); 
int month = cal.get(Calendar.MONTH); 
int year = cal.get(Calendar.YEAR); 

JPanel jPanel = jDayChooser1.getDayPanel(); 

Component component[] = jPanel.getComponents(); 

for(int i=0;i<a.length;i++) { 
    if(month == a[i].getMonth() && year == a[i].getYear()) { 
    component[ a[i].getDay()].setBackground(Color.blue); 
    } 
} 

initComponents(); 
}