pls tell me where the problem is....

i m quite new to java programming...pls tell me the mistake in the following programme...

Code :

class CharStack{
 
	/*Declaration of member variables*/
 
	char[]stackArray;
	int topOfStack;
 
	/*constructor*/
	public void charstack(int capacity){
		stackArray=new char[capacity];
		topOfStack=-1;
		}
 
	/*member methods*/
 
	public void push(char element){
		stackArray[++topOfStack]=element;
		}
	public char pop(){
		return(stackArray[topOfStack--]);
		}
	public boolean isEmpty(){
		return topOfStack<0;
		}
	public char peek(){
		return stackArray[topOfStack];
		}
	public boolean isFull(){
		return topOfStack==stackArray.length-1;
		}
}
 
public class Client{
	CharStack stack=new CharStack(50);
	int i;
	int length=str.length();
 
	BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
	System.out.println("Enter a string:");
	String str=br.readLine();
	System.out.println("Original string:"+str);
 
	for(int i=0;i<length;i++){
		stack.push(str.charAt(i));	
	}
	System.out.pritnln("Reversed string:");
 
	while(!stack.isEmpty()){
		System.out.print(stack.pop());		
		}
	System.out.println();
 
}