Java Simple Calculator class

Package chap;import java.awt.borderlayout;import java.awt.color;import java.awt.flowlayout ;import java.awt.gridlayout;import java.awt.event.actionevent;import  java.awt.event.actionlistener;import java.text.decimalformat;import javax.swing.jbutton;import  javax.swing.jframe;import javax.swing.jpanel;import javax.swing.jtextfield;public class  CALCULATOR&NBSP;{PRIVATE&NBSP;JFRAME&NBSP;FRAME;PRIVATE&NBSP;JPANEL&NBSP;PANEL,PANELKEYS,PANELKEYS_UP, panelkeys_down;private jtextfield textcomputer;//Compute Area private jbutton buttonbk,buttonc;// Backspace and clear 0 key private jbutton button[];//number key group Private jbutton buttondot,buttonaddsub,buttonadd, buttonsub,buttonmul,buttondiv,button1,button2,button3,buttonequal;private double result;// Calculation result private final short add = 1;private final short sub = 2; private final short mul = 3;private final short div = 4;private short operator = -1;//operator public  Calculator () {frame = new jframe ("computer"); Frame.setsize (400, 250);p anel = new  JPanel ();//Global panel panel.setvisible (true); Frame.setvisible (true); Frame.getcontentpane (). Add (panel); Actionlistener listener = new computeractionlistener ();//Key listener//calculation area textcomputer =  new jtextfield (); Textcomputer.settext (""); Textcomputer.seteditable (false); Textcomputer.setbackground (New color (255,255,255));//function key upper half part panelkeys_up = new jpanel (); Panelkeys_up.setlayout (New flowlayout (flowlayout.right)); Buttonbk = new jbutton ("Backspace "); Buttonbk.setforeground (New color (255,0,0)); Buttonc = new jbutton (" C "); Buttonc.setforeground (New color (255,0,0)); Buttonbk.addactionlistener (listener); Buttonc.addactionlistener ( Listener);p Anelkeys_up.add (BUTTONBK);p anelkeys_up.add (BUTTONC);//function key lower halfSub-panelkeys_down = new jpanel ();p anelkeys_down.setlayout (New gridlayout (4,5)); button =  new jbutton[10];for (int i = 0;i < button.length;i++) {button[i] =  new jbutton (integer.tostring (i)); Button[i].setforeground (New color (255,0,0));} Buttonaddsub = new jbutton ("+/-"); Buttonaddsub.setforeground (New color (255,0,0)); buttonAdd  = new jbutton ("+"); Buttonadd.setforeground (New color (255,0,0)); buttonsub = new  jbutton ("-"); Buttonsub.setforeground (New color (255,0,0)); Buttonmul = new jbutton ("*" ); Buttonmul.setforeground (New color (255,0,0)); Buttondiv = new jbutton ("/"); Buttondiv.setforeground (New color (255,0,0)); Button1 = new jbutton ();button2 =  New jbutton (); Button3 = new jbutton (); Button1.setforeground (New color (255,0,0)); Button2.setforeground (New color (255,0,0)); buttOn3.setforeground (New color (255,0,0)); Buttonequal = new jbutton ("="); Buttonequal.setforeground (New color (255,0,0)); Buttonaddsub.addactionlistener (listener); Buttonadd.addactionlistener (listener); Buttonsub.addactionlistener (listener); Buttonmul.addactionlistener ( listener); Buttondiv.addactionlistener (listener); Buttonequal.addactionlistener (listener); for (int i =  0 ; i <=9 ; i++) {Button[i].addactionlistener (listener);} for (int i = 0 ; i <=9 ; i++) {Panelkeys_down.add (button[i]);} Panelkeys_down.add (buttonaddsub);p anelkeys_down.add (buttonadd);p anelkeys_down.add (buttonsub);p Anelkeys_ Down.add (Buttonmul);p anelkeys_down.add (buttondiv);p anelkeys_down.add (buttonequal);p anel.setlayout (new  BorderLayout ());p Anel.add (Textcomputer,borderlayout.north);p anel.add (Panelkeys_up,borderlayout.center); Panel.add (Panelkeys_down,borderlayout.south);} class computeractionlistener implements  actionlistener{@Overridepublic  void actionperformed (actionevent event)  {// TODO  Auto-generated method stubobject keybutton = event.getsource (); String text = textcomputer.gettext ();D Ecimalformat df = new decimalformat (" 0.########### ");//backspaceif (Keybutton == buttonbk && text.length ()  >  0) {Textcomputer.settext (text.substring (0,text.length ()-1));} C Key if (Keybutton == buttonc) {Result = 0;textcomputer.settext ("");} Number key for (int i=0;i<10;i++) {if (Keybutton == button[i]) {textcomputer.settext (text+i);}} if (keybutton == buttonadd) {operator = 1;} if (keybutton == buttonsub) {operator = 2;} if (Keybutton == buttonmul) {operator = 3;} if (keybutton == buttondiv) {operator = 4;} Symbolic key if (keybutton == buttonadd | |  keybutton == buttonsub | |  keybutton == buttonmul | |  keybutton == buttondiv | |  keybutton == buttonequal) {switch (operator) {case add:result +=  Double.parsedouble (text); break;case sub:result -=double.parsedouble (text); Break;case mul:result  *=double.parsedouble (text); break;case div:result /=double.parsedouble (text); Break;default: Result = double.parsedouble (text);} Textcomputer.settext ("");} if (keybutton == buttonequal) {Textcomputer.settext (string.valueof (Result));}}} Public static void main (string args[]) {new calculator ();}}

Java Simple Calculator class