Question

我目前正在尝试构建一个时钟程序来练习构建类和存储文本数据。我当前得到一个nullPointerException，虽然我相信我正确地初始化了TimeClock数组。

public TimeClock[] readFile(){
    try{
        read = new Scanner(new File("TimeClockData.txt") );
    } catch (Exception e){
        System.out.println("could not find file");
    }

    TimeClock[] temp = new TimeClock[100];
    int count = 0;
    String data1;
    String data2;
    String data3;
    while(read.hasNext() ){

        data1 = read.next();
        data2 = read.next();
        data3 = read.next();

        temp[count].setInTime( Long.parseLong(data1) );
        temp[count].setOutTime( Long.parseLong(data2) );
        temp[count].setNotes(data3);

        count++;

    }

    read.close();

    return temp;
}

我一直收到错误：

Exception in thread "main" java.lang.NullPointerException
    at timeclock.pkg2.ReadFile.readFile(ReadFile.java:46)
    at timeclock.pkg2.Timeclock2.main(Timeclock2.java:56)
Java Result: 1

Answer 1

在Java中初始化数组只需创建给定大小的null s数组。在使用之前，您仍需要显式初始化每个元素：

while(read.hasNext() ){

    data1 = read.next();
    data2 = read.next();
    data3 = read.next();

    temp[count] = new TimeClock(); // Was missing in the OP code
    temp[count].setInTime( Long.parseLong(data1) );
    temp[count].setOutTime( Long.parseLong(data2) );
    temp[count].setNotes(data3);

    count++;

}

Answer 2

所有临时数组元素都为null。如果是第一个，你必须初始化它们。

...
temp[count] = new TimeClock(); 
temp[count].setInTime( Long.parseLong(data1) );
...

我该如何解决这个java.lang.NullPointerException错误？

2 个答案: