For Loop with millions of entries - java.lang.OutOfMemoryError: Java heap space

I am getting OutOfMemoryError: Java heap space for the following code:

StringBuilder obj= new StringBuilder("");
InputStream in = new FileInputStream(new File(file));
br = new BufferedReader(new InputStreamReader(in), 102400);
for (String line; (line= br.readLine()) != null;) {
    for (i = 0; i < 3; i++) {
        for (j = 1; j < 5; j++){ 
            obj.append(line.charAt(j)); 
        }
    }   
    hashMap.put(obj.toString(), someValue);
    obj.setLength(0);
}

      

        
        
        
      

    

but

StringBuilder obj= new StringBuilder("");
InputStream in = new FileInputStream(new File(file));
br = new BufferedReader(new InputStreamReader(in), 102400);
for (String line; (line= br.readLine()) != null;) {
    obj.setLength(0);
    for (i = 0; i < 3; i++) {
        for (j = 1; j < 5; j++){ 
            obj.append(line.charAt(j)); 
        }
    }   
    hashMap.put(obj.toString(), someValue);
}

      

        
        
        
      

    

error resolved? What is the problem of placing obj.setLength (0) at the beginning or at the end?

An exception:

Exception in thread "main" java.lang.OutOfMemoryError: Java heap space
at java.util.Arrays.copyOfRange(Unknown Source)
at java.lang.String.<init>(Unknown Source)
at java.io.BufferedReader.readLine(Unknown Source)
at java.io.BufferedReader.readLine(Unknown Source)