Queue implementation in Java Applet Frame

import java.awt.*;

import java.awt.event.*;

import javax.swing.*;

public class que_2 extends JFrame implements ActionListener {

JTextField t1;

String abc="";

JButton b1,b2,b3;

JLabel l1,l3;

int arr[]=new int[50];

int str=0;

int end=0;

que_2()

{

     setTitle("Queue");

     setLayout(new FlowLayout());

     t1=new JTextField(10);

     add(t1);

b1=new JButton("Insert");

add(b1);

b1.addActionListener(this);

b2=new JButton("Remove"); 

add(b2);

b2.addActionListener(this);

b3=new JButton("Exit");   

add(b3);

b3.addActionListener(this);

l1=new JLabel("Message");

//l2=new JLabel("Stack is");

l3=new JLabel();

add(l1);

//add(l2);

add(l3);

//add(l);

}

public static void main(String args[])

{

que_2 f=new que_2();

f.setSize(500, 500);

f.setVisible(true);

 }

public void actionPerformed(ActionEvent ae)

{//int i=9,j=0;

String strn="";

strn=ae.getActionCommand();

if(strn=="Insert")

{

     //l2=new JLabel("");

           //int x;

           if(end!=49)

           {         

           arr[end]=Integer.parseInt(t1.getText());

           t1.setText(null);

           end++;

           }

                else

                {l1.setText("operation can not be performed");}

           for(int i=str;i<end;i++)

           {

                abc=abc+" "+arr[i];

           }

           l3.setText(abc);

           //i--;

           abc="";

}

if(strn=="Remove")

{

     //l2.setText("0");

     if(str!=end)

     {

           str++;

           int x=arr[str];

     //cout<<x<<endl;

}

     else

     {

          

           l1.setText("operation can not be performed");

     }

     for(int i=str;i<end;i++)

     {

           abc=abc+" "+arr[i];

     }

     l3.setText(abc);

     //i--;

     abc="";

}

else if(strn=="Exit")

{

      System.exit(0);    

}

}

}