Java Calculator algorithm implementation

Import Java.awt.BorderLayout;
Import Java.awt.GridLayout;
Import java.awt.event.ActionEvent;
Import Java.awt.event.ActionListener;


Import Javax.swing.JButton;
Import Javax.swing.JFrame;
Import Javax.swing.JPanel;




public class Borderjframe extends JFrame {
Private JButton display;
Private JPanel JP;
Private Boolean start;
Private String Lastcommand;
private double result;
Public Borderjframe () {
This.setlayout (New BorderLayout ());
this.result=0;
This.start=true;
This.lastcommand= "=";
This.display=new JButton ("0");
This.display.setEnabled (FALSE);
Add (display, Borderlayout.north);

ActionListener insert=new insertaction ();
ActionListener command=new commandaction ();
int k=7;
This.setsize (300, 200);
Jp=new JPanel ();
Jp.setlayout (New GridLayout (4, 4));
for (int i=1;i<=4;i++) {
for (int j=1;j<=4;j++) {
if (j==4) {
if (i==1) {
This.addbutton ("/", command);
}else if (i==2) {
This.addbutton ("*", command);
}else if (i==3) {
This.addbutton ("-", command);
}
}else if (i==4) {
This.addbutton ("0", insert);
This.addbutton (".", command);
This.addbutton ("=", command);
This.addbutton ("+", command);
Break
}else{
This.addbutton (String.valueof (k), insert);
k++;
}
}
k=k-6;
}
This.add (Jp,borderlayout.center);
}

Private class Commandaction implements actionlistener{


@Override
public void actionperformed (ActionEvent e) {
String Command=e.getactioncommand ();
if (start) {
if (Command.equals ("-")) {
Display.settext (command);
Start=false;
}else{
Lastcommand=command;
}
}else{
Calculate (Double.parsedouble (Display.gettext ()));
Lastcommand=command;
Start=true;
}
}

}

Private class Insertaction implements actionlistener{


@Override
public void actionperformed (ActionEvent e) {
String Input=e.getactioncommand ();
if (start) {
Display.settext ("");
Start=false;
}
Display.settext (Display.gettext () +input);
}
}

private void AddButton (String Label,actionlistener listener) {
JButton button=new JButton (label);
Button.addactionlistener (listener);
This.jp.add (button);
}

public void calculate (double x) {
if (lastcommand.equals ("+")) result+=x;
else if (lastcommand.equals ("-")) result-=x;
else if (lastcommand.equals ("*")) result*=x;
else if (lastcommand.equals ("/")) Result/=x;
else if (lastcommand.equals ("=")) result=x;
This.display.setText ("+result");
}
}