CODEWITHSUNDEEP
java
mark1092
mark1092

Reputation: 53

randomAccessFile method not writing or reading ints?

I have two methods, one to write 10 ints to a randomAccessFile and one to read the 10 ints. I believe the writer method is not functioning as intended.

Here is my method to write to random file:

try{
                RandomAccessFile file = new RandomAccessFile(nextPath, "rw");
                System.out.println("Writing these ints to file");
                file.seek(0);
                // here I loop 10 times and write the int at position i
                for (int i = 0; i < 10; i++)
                {
                    file.seek(i);
                    toAdd = randInt(1,10);
                    file.writeInt(toAdd);
                    System.out.printf(toAdd + " ");

                }
                file.seek(0);
                System.out.println("");
            }catch(IOException ex){
                System.out.println("Error");
                System.exit(0);}

Here is my method to read the ints:

public int[] readRandom()
    {
        System.out.println("Unsorted ints found in random file:");
        int[] randomInts = new int[10];
        try{        
                RandomAccessFile file = new RandomAccessFile(nextPath, "rw");
                file.seek(0);
                // here I loop 10 times, and read the Int at position i
                for(int i = 0; i < 10; i++)
                {
                    file.seek(i);
                    randomInts[i] = file.readInt();
                    System.out.printf(randomInts[i] + " ");


                }   
                file.seek(0);
                System.out.println("");
            }catch(IOException exc){
                System.out.println("Error reading ints");
                System.exit(0);}
                return randomInts;
            }

Here is my output: Why is only the last int being read?

Writing these ints to file
1 4 5 6 2 4 10 6 5 5 
Unsorted ints found in random file:
0 0 0 0 0 0 0 0 0 5

Upvotes: 0

Views: 834

Answers (2)

davidxxx
davidxxx

Reputation: 131346

Why using a RandomAccessFile to perform sequential writings and sequential readings ? It defeats the purpose of this class.
Besides, you should not shock the caught exceptions but log or trace them.

About your unexpected result, it is caused by not required seek() invocations. You don't need to invoke seek() at each reading or writing operation as readInt() and writeInt() makes the cursor go forward.

I have simplified your sample code to underline the important part :

public void write() {
    try {
        RandomAccessFile file = new RandomAccessFile("temp.txt", "rw");
        System.out.println("Writing these ints to file");
        file.seek(0);
        for (int i = 0; i < 10; i++) {              
            file.writeInt(i);
            System.out.printf(i + " ");
        }           
    } catch (IOException ex) {
        ex.printStackTrace();
        System.exit(0);
    }
}

public int[] readRandom() {
    System.out.println("Unsorted ints found in random file:");
    int[] randomInts = new int[10];
    try {
        RandomAccessFile file = new RandomAccessFile("temp.txt", "rw");
        long filePointer = file.getFilePointer();

        file.seek(0);
        for (int i=0; i<10; i++){
            randomInts[i] = file.readInt();
            System.out.printf(randomInts[i] + " ");
        }               
    } catch (IOException ex) {
        ex.printStackTrace();
        System.exit(0);
    }
    return randomInts;
}

Upvotes: 1

mesbah
mesbah

Reputation: 111

You have missed an important point when you are doing file.seek(i). The seek() method seeks for the byte location you provide and you are incrementing the position to seek by 1. But when you write integers to file it writes 4 bytes for every integers. Your counter should be like this

for (int i = 0; i < 10; i++) {
    file.seek(i*4);
    toAdd = randInt(1,10);
    file.writeInt(toAdd); 
    System.out.printf(toAdd + " ");
 }

And obviously for the read you do this

for (int i = 0; i < 10; i++)
{
    file.seek(i*4);
    randomInts[i] = file.readInt();
    System.out.printf(randomInts[i] + " ");

}

Upvotes: 1

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