[英]I possibly have a Null Pointer Exception, I just don't know where
我正在制作一個簡單代碼生成器(非隨機),但遇到了問題。 用戶將數據輸入到7個文本字段中。 然后將其內容放入String類型的數組中。 然后,我的代碼獲取該數組,分析不同的元素,並吐出一個可用的代碼(對我來說)。
但是,在嘗試標准化String數組(也就是將每個元素都設置為小寫String)時,它導致整個程序停止工作,並且出現了空指針異常。
我的特定錯誤消息如下:
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at inventorycodeconverter.codeDisplay.calculateData(codeDisplay.java:48)
at inventorycodeconverter.InventoryCodeConverterView.button1ActionPerformed(InventoryCodeConverterView.java:315)
at inventorycodeconverter.InventoryCodeConverterView.access$900(InventoryCodeConverterView.java:23)
at inventorycodeconverter.InventoryCodeConverterView$5.actionPerformed(InventoryCodeConverterView.java:211)
at java.awt.Button.processActionEvent(Button.java:392)
at java.awt.Button.processEvent(Button.java:360)
at java.awt.Component.dispatchEventImpl(Component.java:4630)
at java.awt.Component.dispatchEvent(Component.java:4460)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:599)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:269)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:184)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:174)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:169)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:161)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)
似乎造成麻煩的代碼部分是這樣的:
public void calculateData(){
int i;
for (i = 0; i < calculationBuffer.length; i++){ // calculationBuffer is defined and initialized elsewhere.
calculationBuffer[i] = calculationBuffer[i].toLowerCase();// this is line 48 where the first error appears to be.
}
if (calculationBuffer[0].equals("cap")){
displayBuffer[0] = "CAP"; // displayBuffer is defined and initialized elsewhere.
}
else {
displayBuffer[0] = "#Error#";
}
if (calculationBuffer[1].equals("20/400")) {
theTA.append("B");
}
else if (calculationBuffer[1].equals("20/410")){
displayBuffer[1] = "C";
}
else if (calculationBuffer[1].equals("24/410")){
displayBuffer[1] = "F";
}
else if (calculationBuffer[1].equals("24/415")) {
displayBuffer[1] = "Y";
}
else if (calculationBuffer[1].equals("28/400")){
displayBuffer[1] = "H";
}
else if (calculationBuffer[1].equals("28/415")) {
displayBuffer[1] = "X";
}
else if (calculationBuffer[1].equals("28/410")) {
displayBuffer[1] = "I";
}
else if (calculationBuffer[1].equals("33/400")) {
displayBuffer[1] = "J";
}
else if (calculationBuffer[1].equals("38/400")) {
displayBuffer[1] = "K";
}
else if (calculationBuffer[1].equals("43/400")) {
displayBuffer[1] = "M";
}
else if (calculationBuffer[1].equals("45/400")) {
displayBuffer[1] = "N";
}
else if (calculationBuffer[1].equals("58/400")) {
displayBuffer[1] = "Q";
}
else if (calculationBuffer[1].equals("70/400")) {
displayBuffer[1] = "S";
}
else if (calculationBuffer[1].equals("89/400")) {
displayBuffer[1] = "T";
}
}
public void displayData() {
String displayString;
displayString = Arrays.toString(displayBuffer);
StringTokenizer st = new StringTokenizer(displayString, ",");
while(st.hasMoreTokens()){
String finalText = st.nextToken();
theTA.append(finalText);
}
}
在某處您已聲明數組如下(可能):
String[] calculationBuffer = new String[size];
它將使用null
初始化所有索引。 因此,您將獲得NPE。
在使用數組之前,應按如下所示將所有索引填充到循環中
for(int i=0; i<size; i++)
{
calculationBuffer[i] = "A String";
}
如果要像這樣聲明字符串數組,則String[] calculationBuffer = new String[size];
那么所有的字符串元素都將由Null初始化,因此,如果您不在其他地方的此字符串數組中添加值,則可以像這樣更新代碼
for (i = 0; i < calculationBuffer.length; i++){
**calculationBuffer[i]="";**
calculationBuffer[i] = calculationBuffer[i].toLowerCase();// this is line 48 where the first error appears to be.
}
謝謝
您在哪里填充您的CalculationBuffer?
您得到的錯誤指示CalculationBuffer [i]為null,表示您沒有正確填充初始數組。
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