java - How do I get the buttons on my calculator to actually do equations? -


i wanted make small calculator project fun test out new gui knowledge java swing api. created gui, there's crucial part missing: math! question is, how add functionality each of these buttons? in simpler terms: how make buttons add text box(2+2) when user clicks buttons, , have system add numbers , display them user?

here's code: 

package calculatorpack;  import java.awt.borderlayout; import java.awt.color; import java.awt.gridbagconstraints; import java.awt.gridbaglayout; import java.awt.event.actionevent; import java.awt.event.actionlistener;  import javax.swing.boxlayout; import javax.swing.jbutton; import javax.swing.jframe; import javax.swing.jlabel; import javax.swing.jpanel; import javax.swing.jtextarea; import javax.swing.uimanager;   public class basiccalculatordesign {       public static void main(string[] args) {         try {             uimanager.setlookandfeel(uimanager.getsystemlookandfeelclassname());             }              catch (exception e) {             }         basiccalculatordesign calc = new basiccalculatordesign();         calc.start();     }       jtextarea input = new jtextarea();     string[] operators;     int[] numbers;      public void start() {         jframe frame = new jframe();         jpanel panel = new jpanel();         jbutton 1 = new jbutton("1");         jbutton 2 = new jbutton("2");         jbutton 3 = new jbutton("3");         jbutton 4 = new jbutton("4");         jbutton 5 = new jbutton("5");         jbutton 6 = new jbutton("6");         jbutton 7 = new jbutton("7");         jbutton 8 = new jbutton("8");         jbutton 9 = new jbutton("9");         jbutton 0 = new jbutton("0");         jbutton plus = new jbutton("+");         jbutton minus = new jbutton("-");         jbutton divide = new jbutton("/");         jbutton multiply = new jbutton("*");         jbutton sqrt = new jbutton("sqrt");         jbutton percentage = new jbutton("%");         jbutton equals = new jbutton("=");          // work on           jlabel label = new jlabel("basic calculator");         frame.getcontentpane().add(borderlayout.north, label);          frame.getcontentpane().add(borderlayout.south, input);          panel.setbackground(color.blue);         panel.setlayout(new gridbaglayout());          jpanel panel2 = new jpanel();         panel2.setlayout(new boxlayout(panel2, boxlayout.y_axis));         panel2.setbackground(color.red);         frame.getcontentpane().add(borderlayout.east, panel2);          frame.getcontentpane().add(borderlayout.center, panel);          frame.setdefaultcloseoperation(jframe.exit_on_close);         frame.setvisible(true);         frame.setsize(210, 260);           gridbagconstraints right = new gridbagconstraints();         right.anchor = gridbagconstraints.west;         gridbagconstraints left = new gridbagconstraints();         left.anchor = gridbagconstraints.east;         gridbagconstraints middle = new gridbagconstraints();         middle.anchor = gridbagconstraints.center;         right.gridwidth = gridbagconstraints.remainder;         right.fill = gridbagconstraints.horizontal;          // add buttons         panel.add(one, left);         panel.add(two, middle);         panel.add(three, right);         panel.add(four, left);         panel.add(five, middle);         panel.add(six, right);         panel.add(seven, left);         panel.add(eight, middle);         panel.add(nine, right);         panel.add(zero, right);          panel2.add(equals);         panel2.add(plus);         panel2.add(minus);         panel2.add(divide);         panel2.add(multiply);         panel2.add(sqrt);         panel2.add(percentage);          //integrate buttons          one.addactionlistener(new buttonlistener());         two.addactionlistener(new buttonlistener());         three.addactionlistener(new buttonlistener());         four.addactionlistener(new buttonlistener());         five.addactionlistener(new buttonlistener());         six.addactionlistener(new buttonlistener());         seven.addactionlistener(new buttonlistener());         eight.addactionlistener(new buttonlistener());         nine.addactionlistener(new buttonlistener());         zero.addactionlistener(new buttonlistener());          equals.addactionlistener(new operatorlistener());         }       class buttonlistener implements actionlistener {         public void actionperformed(actionevent e) {             jbutton source = (jbutton)e.getsource();             input.replaceselection(source.getactioncommand());            }     }      class operatorlistener implements actionlistener {         public void actionperformed(actionevent e) {             jbutton source2 = (jbutton)e.getsource();             input.replaceselection(source2.getactioncommand());          }     }      // need math.      class equalslistener implements actionlistener {         public void actionperformed(actionevent e) {           }     } }

it looks want evaluate arithmetic expression. options:


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