Exercise 1
public class Matrix {

	private int n;
	private int m;
	int[][] mat;
	
	public SymmetricMatrix(int n, int m)
	{
		this.n = n;
		this.m = m;
	}

	public void printMatrix()
	{
		for (int i =0;i<n;i++)
		{
			for (int j=0;j<m;j++)
			{
				System.out.print( mat[i][j]+"  ");
			}
			System.out.println("");
		}
	}
}


Exercise 2
import java.util.*;
public class StringStack {
		private ArrayList<String> a;
		
		public StringStack() {
			a = new ArrayList<String>();
		}
		public boolean isEmpty(){
		return a.size()== 0;
		}
		
		public void push(String o){
		a.add(o);
		}
		
		public String pop(){
		Object temp = a.get(a.size()-1);
		a.remove(a.size()-1);
		return (String)temp;
		}
		
		public static boolean palindrome(String word) {
		StringStack s = new StringStack();
		String reverse = "";
		for (int i = 0; i < word.length(); i++)
		s.push(word.substring(i, i + 1));
		while (!s.isEmpty())
		reverse += s.pop();
		return word.equals(reverse);
		}
}

Stacks Queues
1. Stack
2. Queue
3. Queue
4. Queue
5. Stack