CODEWITHSUNDEEP
java
EldaSummer
EldaSummer

Reputation: 27

Java Tutorial, this program contains a bug but I could not find it

This program complies but won't run successfully, I am unable to find the bug.

public class Q1 {
    public static void main(String[] args) {
        StringBuffer[]stringBuffers = new StringBuffer[10];

        for(int i =0; i< stringBuffers.length;i++){
            stringBuffers[i].append("StringBuffer at index " + i);
        }
    }
}

Upvotes: 0

Views: 188

Answers (4)

a Learner
a Learner

Reputation: 5042

IN the statement:

StringBuffer[]stringBuffers = new StringBuffer[10];

you have just created an array of 10 elements. But you have not put any element in it.Each element in this array is still empty and by default, contains null.

So when you called 

stringBuffers[i].append("StringBuffer at index " + i);

here stringBuffers[i] is still uninitialized and is pointing to null.

So it is giving java.lang.NullPointerException.

As stated in other answers, if you do like this:

for(int i =0; i< stringBuffers.length;i++){
   stringBuffers[i] = new StringBuffer();

This will initialize each element of stringBuffer array with the reference to a StringBuffer object.So stringBuffer[i] now is not empty.

By the way You should use StringBuilder. Both StringBuffer and StringBuilder provides mutable strings. Use StringBuffer only if your application is running in multithreading environment becoz it introduces performance overhead

Upvotes: 1

Lo Juego
Lo Juego

Reputation: 1325

You need to init the StringBuffer:

public class Q1 {
public static void main(String[] args) {
    StringBuffer[]stringBuffers = new StringBuffer[10];

    for(int i =0; i< stringBuffers.length;i++){
        stringBuffers[i]= new StringBuffer();
        stringBuffers[i].append("StringBuffer at index " + i);
    }
}
}

Upvotes: 2

Rohit Jain
Rohit Jain

Reputation: 213261

You need to initialize the StringBuffer objects in your array with the required String: -

for(int i =0; i< stringBuffers.length;i++){
    stringBuffers[i] = new StringBuffer("StringBuffer at index " + i);

}

Upvotes: 1

Denys S&#233;guret
Denys S&#233;guret

Reputation: 382160

You don't initialize your stringbuffers.

You should have something like 

for(int i =0; i< stringBuffers.length;i++){
   stringBuffers[i] = new StringBuffer();

or

for(int i =0; i< stringBuffers.length;i++){
   stringBuffers[i] = new StringBuffer("StringBuffer at index " + i);

Upvotes: 6

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