使用 getText() 将字符串从 Java 表单复制到字符串数组中的异常

Question

I'm getting a NullPointerException with the following Java code:

static String s[],t[],temp;

private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {                                         
    // TODO add your handling code here:
    s[0]=jTextField2.getText();
    jTextField3.setText("The input string is: "+s[0]);
    temp=jTextField1.getText();
    t=temp.split(" ");
    jTextField3.setText("The input string is: "+t[0]);
}

This code keeps giving me java.lang.NullPointerException . What is wrong with my code???

I also tried this way:

static String s[],t[],temp;

private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {                                         
    // TODO add your handling code here:
    temp=jTextField2.getText();
    s[0]=temp;
    jTextField3.setText("The input string is: "+s[0]);
    temp=jTextField1.getText();
    //t=temp.split(" ");
    //jTextField3.setText("The input string is: "+t[0]);
}

And also jTextField3.setText("The input string is: "+t); doesn't work with t declared just as static String t. in the text field it shows some exception again.

Answer 1

You're declaring your array, but you're never initializing it, and so when you try to access the array items, for instance like so, s[0] , a NPE will be thrown since s is null.

You need to assign the array to an array object like so:

// SIZE is an int constant that is the size of the array you desire.
String[] s = new String[SIZE];

Side notes:

• You likely should not declare any of these variables as static, and doing so suggests that the program design could be improved.
• I have to wonder if you are using parallel arrays to hold your data. If so, consider creating a new class to hold each "row" of data's information, and then using an ArrayList of this type of class.

---

Edit You state:

But I dunno the size initially. Can I use String[temp.length];???

You could initialize your arrays to a large size, one that's likely to be larger than you expect to need, however an even better solution is to not use arrays at all (directly) but rather use ArrayLists which behave sort-of kind-of like arrays of variable size.

Answer 2

int LENGTH = 10;
static String s[] = new String[LENGTH];
static String t[] = new String[LENGTH];