required "EXIT" button and dot(".") operartion. and floating convertion for "1/x" botton, float variable "<-"backspace

Question

I used Float.parseFloat and all int variable with float then backspace won't work properly

// packets that are required
import java.applet.*;
import java.awt.*;
import java.awt.event.*;
//NewCalculator class
public class NewCalculator extends Applet implements ActionListener{
    String cmd[]={"+","-","*","/","=","C","%","<-","1/x","."};
    String cmd1[] = {"MR","MS","EXIT"};
    int pv=0,r=0;   
    String op="";
    Button b[]=new Button[23];
    TextField t1=new TextField(10);
        // applet initialization
    public void init(){
        setLayout(new BorderLayout());
        add(t1,"North");
        t1.setText("0");
        Panel p=new Panel();
        p.setLayout(new GridLayout(4,4));

        for(int i=0;i<20;i++){
            if(i<10)
                b[i]=new Button(String.valueOf(i));
            else
                b[i]=new Button(cmd[i%10]);
            b[i].setFont(new Font("Arial",Font.BOLD,25));
            p.add(b[i]);
            add(p,"Center");
            b[i].addActionListener(this);
        }

        b[20] = new Button("MR");
        b[20].setFont(new Font("Arial",Font.BOLD,25));
        p.add(b[20]);
        b[20].addActionListener(this);

        b[21] = new Button("MS");
        b[21].setFont(new Font("Arial",Font.BOLD,25));
        p.add(b[21]);
        b[21].addActionListener(this);

        b[22] = new Button("EXIT");
        b[22].setFont(new Font("Arial",Font.BOLD,25));
        p.add(b[22]);
        b[22].addActionListener(this);
    }   
        // actionperformer for the button and textfield
    public void actionPerformed(ActionEvent ae){
        int res=0;              
        if(op == "EXIT"){   // exit is not working  
            System.out.println("1");
            System.exit(0);
            System.out.println("2");
        }
        else{
            String cap=ae.getActionCommand();
            int cv=Integer.parseInt(t1.getText());
            if(cap.equals("C")){
                t1.setText("0");
                pv=0;
                cv=0;
                res=0;
                op="";
            }
            else if(cap.equals("=")){
                res=0;
                if(op=="+")
                res=pv+cv;
                else if(op=="-")
                    res=pv-cv;
                else if(op=="*")
                    res=pv*cv;
                else if(op=="/")
                    res=pv/cv;
                else if(op=="%")
                    res=pv%cv;

                t1.setText(String.valueOf(res));
            }
            else if(cap.equals("+")||cap.equals("-")||cap.equals("*")||cap.equals("/")||cap.equals("%")||cap.equals("<-")||cap.equals("1/x")||cap.equals(".")||cap.equals("MS")||cap.equals("MR")){
                pv=cv;
                op=cap;
                t1.setText("0");
                if(op=="<-"){ // doesn't works with float
                        if(pv !=0){
                            pv = pv /10;
                            t1.setText("");                     
                        }
                        else{
                            cv = cv /10;
                            t1.setText(""+cv);
                        }
                }
                if(op == "1/x"){ // not able to do with floatnumber
                    pv =1/pv;
                    t1.setText(""+pv);

                }
                if(op == "MS"){             
                    r = cv ;                
                }
                if(op == "MR"){
                    t1.setText(""+r);
                }               
            }       
            else{
                int v=cv*10+Integer.parseInt(cap);
                t1.setText(String.valueOf(v));
            }

        }
    }
}