最终效果图：
完整项目代码：
package First_App;import java.awt.*;import java.awt.event.*;import javax.swing.*;public class Caculator extends JFrame{/** 图形化界面设计* */private static final long serialVersionUID = 4907149509182425824L;public Caculator(){Container c = getContentPane(); //定义一个顶级容器csetLayout(new GridLayout(2,1));//新建网格布局管理器，2行1列JTextField jtf = new JTextField("0",40);//构造一个用指定文本和列初始化的新文本框--jtfjtf.setHorizontalAlignment(JTextField.RIGHT);//设置水平对齐方式：居右对齐JButton data0 = new JButton("0");JButton data1 = new JButton("1");JButton data2 = new JButton("2");JButton data3 = new JButton("3");JButton data4 = new JButton("4");JButton data5 = new JButton("5");JButton data6 = new JButton("6");JButton data7 = new JButton("7");JButton data8 = new JButton("8");JButton data9 = new JButton("9");JButton point = new JButton(".");JButton equ = new JButton("=");JButton plus = new JButton("+");JButton minus = new JButton("-");JButton mtp = new JButton("*");JButton dvd = new JButton("/");JButton sqr = new JButton("sqrt");JButton root = new JButton("x^2");JButton tg = new JButton("退格");JButton ql = new JButton("清零");JPanel jp = new JPanel(); //新建JPanel面板--jpjp.setLayout(new GridLayout(4,5,5,5));//新建网格布局管理器（行数，列数，组件间的水平垂直间距）jp.add(data7);jp.add(data8);jp.add(data9);jp.add(plus);jp.add(sqr);jp.add(data4);jp.add(data5);jp.add(data6);jp.add(minus);jp.add(root);jp.add(data1);jp.add(data2);jp.add(data3);jp.add(mtp);jp.add(ql);jp.add(data0);jp.add(point);jp.add(equ);jp.add(dvd);jp.add(tg);c.add(jtf);//将文本框jtf添加到顶级容器c中c.add(jp);//将JPanel面板jp添加到顶级容器c中setSize(400,300);setTitle("计算器");setVisible(true);setResizable(false);//窗体大小由程序员决定，用户不能自由改变大小setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);/** ********************************************************** 相关计算功能的实现 * ********************************************************** */data0.addActionListener(new ActionListener(){//数字0的输入public void actionPerformed(ActionEvent arg0){if(jtf.getText().equals("0")){//将按钮值与0作比较jtf.requestFocus();//把输入焦点放在调用这个方法的控件上(即把光标放在文本框jtf里)}else{String str = jtf.getText();//取得当前按钮的按钮值jtf.setText(str+"0"); //将文本内容后加上字符0}}});data1.addActionListener(new ActionListener(){//数字1的输入public void actionPerformed(ActionEvent arg0){if(jtf.getText().equals("0")){//将按钮值与0作比较jtf.setText("");//将文本框初始化为空jtf.setText("1");//将文本框内容置为 1jtf.requestFocus();//把输入焦点放在调用这个方法的控件上(即把光标放在文本框jtf里)}else{String str = jtf.getText();//取得当前按钮的按钮值jtf.setText(str+"1"); //将文本内容后加上字符1}}});data2.addActionListener(new ActionListener(){public void actionPerformed(ActionEvent arg0){if(jtf.getText().equals("0")){jtf.setText("");jtf.setText("2");jtf.requestFocus();}else{String str = jtf.getText();jtf.setText(str+"2");}}});data3.addActionListener(new ActionListener(){public void actionPerformed(ActionEvent arg0){if(jtf.getText().equals("0")){jtf.setText("");jtf.setText("3");jtf.requestFocus();}else{String str = jtf.getText();jtf.setText(str+"3");}}});data4.addActionListener(new ActionListener(){public void actionPerformed(ActionEvent arg0){if(jtf.getText().equals("0")){jtf.setText("");jtf.setText("4");jtf.requestFocus();}else{String str = jtf.getText();jtf.setText(str+"4");}}});data5.addActionListener(new ActionListener(){public void actionPerformed(ActionEvent arg0){if(jtf.getText().equals("0")){jtf.setText("");jtf.setText("5");jtf.requestFocus();}else{String str = jtf.getText();jtf.setText(str+"5");}}});data6.addActionListener(new ActionListener(){public void actionPerformed(ActionEvent arg0){if(jtf.getText().equals("0")){jtf.setText("");jtf.setText("6");jtf.requestFocus();}else{String str = jtf.getText();jtf.setText(str+"6");}}});data7.addActionListener(new ActionListener(){public void actionPerformed(ActionEvent arg0){if(jtf.getText().equals("0")){jtf.setText("");jtf.setText("7");jtf.requestFocus();}else{String str = jtf.getText();jtf.setText(str+"7");}}});data8.addActionListener(new ActionListener(){public void actionPerformed(ActionEvent arg0){if(jtf.getText().equals("0")){jtf.setText("");jtf.setText("8");jtf.requestFocus();}else{String str = jtf.getText();jtf.setText(str+"8");}}});data9.addActionListener(new ActionListener(){public void actionPerformed(ActionEvent arg0){if(jtf.getText().equals("0")){jtf.setText("");jtf.setText("9");jtf.requestFocus();}else{String str = jtf.getText();jtf.setText(str+"9");}}});point.addActionListener(new ActionListener(){ //点号的输入public void actionPerformed(ActionEvent arg0){if(jtf.getText().equals("0")){jtf.setText("");jtf.setText(".");jtf.requestFocus();}else{String str = jtf.getText();jtf.setText(str+".");}}});plus.addActionListener(new ActionListener(){ //+号的输入public void actionPerformed(ActionEvent arg0){if(jtf.getText().equals("0")){jtf.setText("");jtf.setText("+");jtf.requestFocus();}else{String str = jtf.getText();jtf.setText(str+"+");}}});minus.addActionListener(new ActionListener(){ //-号的输入public void actionPerformed(ActionEvent arg0){if(jtf.getText().equals("0")){jtf.setText("");jtf.setText("-");jtf.requestFocus();}else{String str = jtf.getText();jtf.setText(str+"-");}}});mtp.addActionListener(new ActionListener(){ //*号的输入public void actionPerformed(ActionEvent arg0){if(jtf.getText().equals("0")){jtf.setText("");jtf.setText("*");jtf.requestFocus();}else{String str = jtf.getText();jtf.setText(str+"*");}}});dvd.addActionListener(new ActionListener(){ //除号的输入public void actionPerformed(ActionEvent arg0){if(jtf.getText().equals("0")){jtf.setText("");jtf.setText("/");jtf.requestFocus();}else{String str = jtf.getText();jtf.setText(str+"/");}}});//【**退格功能如下**】tg.addActionListener(new ActionListener(){//监听退格键public void actionPerformed(ActionEvent arg0){//处理退格键被按下的事件String text = jtf.getText();int i = text.length();if(i>0){text = text.substring(0,i-1);//去掉最后一个字符if (text.length() == 0) {// 如果文本没有了内容，则初始化计算器的各种值jtf.setText("0");} else { // 显示新的文本jtf.setText(text);}}}});//【**清零功能如下**】ql.addActionListener(new ActionListener(){//监听清零键public void actionPerformed(ActionEvent e) {jtf.setText("0");//将文本框置为0（清零功能）}});//【**平方功能如下**】root.addActionListener(new ActionListener(){//监听root键public void actionPerformed(ActionEvent e){//root键被按事件String i = jtf.getText();Double j = Double.parseDouble(i);//将字符串i转换成对应的double类型的数值double ans = j*j; //求平方String answer =String.valueOf(ans);//将int型数据转换成String类型jtf.setText(answer);//将文本框设置为平方后的结果}});//【**开方功能如下**】sqr.addActionListener(new ActionListener(){//监听sqrt键public void actionPerformed(ActionEvent e){//sqrt键被按事件String i = jtf.getText();Double j = Double.parseDouble(i);//将字符串转换成对应的double类型的数值double ans = (double)Math.sqrt(j);//求开方String answer = String.valueOf(ans);//将double型数据转换成String类型jtf.setText(answer);//将文本框设置为开方后的结果}});//【等号实现 加减乘除 功能】equ.addActionListener(new ActionListener(){ //监听 “等号” 按键public void actionPerformed(ActionEvent arg0){//处理“等号” 按键被按下事件//【**加法运算**】if(jtf.getText().indexOf("+")!= -1){//将字符串分割为子字符串，然后将结果作为字符串数组返回String[] s = jtf.getText().split("[+]");//转义字符，要用"[+]"或者"\+"Double d1 = Double.parseDouble(s[0]);//返回一个指定字符串表示的double值Double d2 = Double.parseDouble(s[1]);double ans = d1 + d2;String answer = String.valueOf(ans);//将结果转换为字符串jtf.setText(answer);//将加法运算的结果以字符串形式在文本框中显示}//【**减法运算**】else if(jtf.getText().indexOf("-")!= -1){String[] s = jtf.getText().split("-");jtf.setText("");Double d1 = Double.parseDouble(s[0]);Double d2 = Double.parseDouble(s[1]);double ans = d1-d2;String answer =String.valueOf(ans);jtf.setText(answer);}//【**乘法运算**】else if(jtf.getText().indexOf("*")!= -1){String[] s = jtf.getText().split("[*]");//*是转义字符，要用"[*]",或者"\*"jtf.setText("");Double d1 = Double.parseDouble(s[0]);Double d2 = Double.parseDouble(s[1]);double ans = d1*d2;String answer =String.valueOf(ans);jtf.setText(answer);}//【**除法运算**】else if(jtf.getText().indexOf("/")!= -1){String[] s = jtf.getText().split("/");jtf.setText("");Double d1 = Double.parseDouble(s[0]);Double d2 = Double.parseDouble(s[1]);double ans = d1/d2;String answer =String.valueOf(ans);jtf.setText(answer);}else{jtf.setText("请选择要进行的运算");}}});}public static void main(String[] args) {new Caculator();}}
