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As per my understanding 'Exception handling' use Template method design pattern.

'Template method design pattern defines the skeleton of an algorithm in a method, deferring some steps to subclasses. Template Method lets subclasses redefine certain steps of an algorithm without changing the algorithms structure.'

If we see the API source code, Exception handling class in each hierarchy add its own method on the top of parent class.

Agree with hprem991. Could you please clear the requirement?What I have understood. you have the colour as below
{a,a,g,d,v,c,s,d,f,r,h,w,s,r,t,g,f,d,s,d,h}. and you have to arrange like
{a,a,a,a,a,a,a,b,b,b,b,b,b,c,c,c,c,c.....}
Also the accepted space time complexity ....

import java.util.Arrays;



public class TestLoop {
public static void main(String[] args) {
char[] a = {'G','O'};
char[] b = {'G','O','O','G','L','E'};

//remove the duplicate as {' ',' ',' ',' ','L','E'};
for(int i=0;i<a.length;i++){
for(int j=0;j<b.length;j++){
if(a[i]==b[j]){
b[j]=' ';
}
}
}

// move the ' ' to end.. as {'L','E',' ',' ',' ',' '}
for(int k=0;k<b.length ;k++){
for(int l=k+1;l<b.length;l++)
if(b[k] == ' ' && b[l] != ' ' ){
b[k] = b[l];
b[l] = ' ';
}
}
// now search the first position of ' ' and create sub array from 0 to ii th position
for(int ii=0;ii<b.length;ii++){
if(b[ii] == ' '){
b = Arrays.copyOfRange(b, 0, ii);
break;
}
}

for(int kk=0;kk<b.length;kk++)
System.out.println("-----------:" + b[kk]);
}
}

The safest way is to ensure that only one thread calls into the third-party library at a time - that is, take a mutex around EVERY call to the library. Making it so that multiple threads can use the library at once. This could be implemented using Semaphore.

class Pool {
//you have only one instance.
private static final MAX_AVAILABLE = 1;

private final Semaphore available = new Semaphore(MAX_AVAILABLE, true);

public Object getItem() throws InterruptedException {
available.acquire();
return getNextAvailableItem();
}

public void putItem(Object x) {
if (markAsUnused(x))
available.release();
}

// Not a particularly efficient data structure; just for demo

protected Object[] items = <your third pary library item here.>
protected boolean[] used = new boolean[MAX_AVAILABLE];

protected synchronized Object getNextAvailableItem() {
for (int i = 0; i < MAX_AVAILABLE; ++i) {
if (!used[i]) {
used[i] = true;
return items[i];
}
}
return null; // not reached
}

protected synchronized boolean markAsUnused(Object item) {
for (int i = 0; i < MAX_AVAILABLE; ++i) {
if (item == items[i]) {
if (used[i]) {
used[i] = false;
return true;
} else
return false;
}
}
return false;
}

}

http://docs.oracle.com/javase/1.5.0/docs/api/index.html?java/util/concurrent/Semaphore.html

public class Test {
public static void main(String[] args) {

char[] charArr ={'a','b','a','a','c','d',' ','a','e','a','c','b','b','f','g',' '};
//remove the duplicate char by ' '
for(int i=0;i<charArr.length;i++){
for(int j=0;j<charArr.length;j++){
if((i!=j)&& charArr[i] != ' ' && charArr[i]==charArr[j]){
charArr[j] = ' ';
}
}
}
// push the blank to end
for(int k=0;k<charArr.length ;k++){
for(int l=k+1;l<charArr.length;l++)
if(charArr[k] == ' ' && charArr[l] != ' ' ){
charArr[k] = charArr[l];
charArr[l] = ' ';
}
}
for(int ii=0;ii<charArr.length;ii++){
System.out.println("-----------: " + charArr[ii]);
}
}

}

Time complexity is O(n^2)

I forgot to mention that , I was told not to use any collection framework

As file size is very very big, say more than 2 GB, I feel above code is not much efficient.It will take longer time. Instead reading a single file , I would split the file into n number of small files based on the line count. Then , will run your processing logic in a multithread environment , will use fixed thread pool instead of creating many threads. I will use concurrent hash map instead HashMap<String,Interger> to store the word and count.