JAVA计算器算法实现

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);
}
}

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