新人写了半天的东西分享一下，求点击求分。。 - 黑马程序员技术交流社区

for(int i = 0;i < 100; i ++){
int x = i + 1;
//....
}

复制代码

public class MyMainAlgorithm {
public MyMainAlgorithm(){}
/**
* 暴露出去的方法，本类仅有这一个public方法，其他方法都为此方法服务
* @param str 从输入文本框获取的计算表达式
* @return 计算的结果，字符串形式
*/
public String getAnswer(String str){
//输入为空不计算，比如不输入就直接点“=键”
if(str == null || str.equals(""))
return "0.";
String ans = "";
//首先判断表达式中的括号是否匹配
if(!isWellBracket(str))
ans = "输入的表达式括号不匹配";
//判断是否为正确的表达式，防止类似连续两个+号的情况等等
//.....
//到此假设字符串已经合法 =.= 偷懒了。。
//中缀表达式变为后缀表达式,用Stack模拟栈
Stack<String> preAns = changeToHouzhui(str);
//计算这个后缀表达式
ans = calculat(preAns) + "";
return ans;
}
private double calculat(Stack<String> preAns){
double ans = 0.0;
//倒置栈
Stack<String> ss = new Stack<String>();
while(!preAns.isEmpty())
ss.push(preAns.pop());
//从表达式栈取出数字压入结果栈，取的是操作符就取出两个元素计算
Stack<Double> sd = new Stack<Double>();
String str;
while(!ss.isEmpty()){
str = ss.pop();
//是操作符就把结果栈的数字取出来两个进行操作，
//注意原栈倒置过，现在取出又压入了结果栈，又从结果栈拿出进行计算，所以后取出的是操作数
//先从sd中取出的是被操作数。
if(str.length() == 1 && isOperator(str.charAt(0))){
sd.push(bind(sd.pop(),sd.pop(),str.charAt(0)));
}else{//不是操作符就把数压入结果栈
sd.push(new Double(str));
}
}
ans = sd.peek().doubleValue();
return ans;
}
private Double bind(Double d2,Double d1,char op){
Double res = null;
switch(op){
case '+':
res = d1+d2;
break;
case '-':
res = d1-d2;
break;
case '*':
res = d1*d2;
break;
case '/':
res = d1/d2;
break;
}
return res;
}
//中缀表达式转成后缀表达式
private Stack<String> changeToHouzhui(String str){
//System.out.println(str);
//--------------------------
//将数和操作符分开 ,存在队列中
LinkedList<String> queue = new LinkedList<String>();
StringBuilder num = new StringBuilder();
for(int i = 0;i < str.length();i ++){
char c = str.charAt(i);
if(!isOperator(c)){
num.append(c);
}else{
if(num.length() != 0){
queue.addLast(num.toString());
num.delete(0, num.length());
}
queue.addLast(c+"");
}
}
if(num.length() != 0)
queue.addLast(num.toString());
//System.out.println(queue);
//------------------------
//开始转换
Stack<String> numStack = new Stack<String>();//存后缀表达式的栈
Stack<String> operatorStack = new Stack<String>();//存操作符的栈
Iterator<String> is = queue.iterator();
while(is.hasNext()){
String s = is.next();
if(s.equals("(")){
operatorStack.push(s);
}
else if(s.equals(")")){
while(!operatorStack.empty() && !operatorStack.peek().equals("("))
numStack.push(operatorStack.pop());
if(!operatorStack.empty())
operatorStack.pop();//弹出"("
}else if(s.equals("+") || s.equals("-")){
if(operatorStack.empty() || operatorStack.peek().equals("("))
operatorStack.push(s);
else{
while(!operatorStack.empty() && !operatorStack.peek().equals("(")){
numStack.push(operatorStack.pop());
}
operatorStack.push(s);
}
}else if(s.equals("*") || s.equals("/")){
if(operatorStack.empty() ||
operatorStack.peek().equals("+") ||
operatorStack.peek().equals("-")||
operatorStack.peek().equals("(")){
operatorStack.push(s);
}else{
numStack.push(operatorStack.pop());
operatorStack.push(s);
}
}else{
numStack.push(s);
}
}
while(!operatorStack.empty()){//如果操作符栈中还有，就都压入表达式栈
if(!operatorStack.peek().equals("(")){
numStack.push(operatorStack.pop());
}
}
//System.out.println(numStack);
return numStack;
}
private boolean isOperator(char c){
if(c >= '0' && c <= '9' || c == '.')
return false;
return true;
}
/**
* 检查输入字符串中的括号是否匹配
* 可以利用栈简单实现，
* 即遇到'('进栈，遇到')'就从栈中弹出一个元素，直到表达式结束。
* 如果栈为空则表示括号匹配，否则不匹配
*
* @param str
* @return
*/
private boolean isWellBracket(String str){
Stack<String> stack = new Stack<String>();
for(int i = 0;i < str.length();i ++){
char c = str.charAt(i);
if(c == '(')
stack.push(c+"");
else if(c == ')'){
if(stack.isEmpty())
return false;
stack.pop();
}
}
return stack.isEmpty();
}
}

复制代码

public class MyWindow extends JFrame {
private JTextField jti = new JTextField(20);// 输入文本框
private JTextField jto = new JTextField(20);//显示结果的文本框
private JButton[] jb = new JButton[27];
private String[] arr = {"7", "8", "9", "/", "CE",
"4", "5", "6", "*","(","1","2","3", "+",")","0",".","C","-","=" };
private JPanel jp = new JPanel();// 主面板
private JPanel m = new JPanel();// 次面板
private GridLayout glo = new GridLayout(6, 1, 3, 3);// 主网格布局
private GridLayout glo1 = new GridLayout(1, 5, 4, 4);// 次网格布局
protected MyWindow(){}
//初始化界面，传入一个键盘监听类和动作监听类
protected void init(KeyListener kl,ActionListener al) {}
//得到输入的表达式字符串
protected String getInput(){}
//在文本框里显示字符串
protected void setAnswer(String ans){}
//清除输入，比如点击"CE"键
protected void clearInput(){}
//回退一个输入，比如点击"C"键
protected void backspace(){}
//向输入文本框里输入字符串
protected void type(String str){}
}

复制代码

public class MyActionListener implements ActionListener{
private MyWindow mw;
protected MyActionListener(MyWindow my){
this.mw = my;
}
/**
* 点击按钮动作
*/
@Override
public void actionPerformed(ActionEvent e) {
// TODO Auto-generated method stub
JButton btn = (JButton)e.getSource();
String cmd = btn.getText();
if("=".equals(cmd)){
//点击=按钮时计算结果
MyMainAlgorithm mma = new MyMainAlgorithm();
String str = mma.getAnswer(mw.getInput());
mw.setAnswer(str);//将结果显示在结果文本框里
}else if("CE".equals(cmd)){
mw.clearInput();//清空输入
}else if("C".equals(cmd)){
mw.backspace();//回退一个字符
}else{
mw.type(cmd);
}
}
}

复制代码

public class MyKeyListener extends KeyAdapter {
private MyWindow mw;
protected MyKeyListener(MyWindow my){
this.mw = my;
}
/**
* 在输入框里按下字符处理code
*/
@Override
public void keyTyped(KeyEvent e) {
// TODO Auto-generated method stub
//懒的写了，直接截死了。
mw.setAnswer("懒的写键盘处理code了，就用鼠标点把。");
new Thread(new Runnable(){
@Override
public void run() {
// TODO Auto-generated method stub
try {
Thread.sleep(900);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
mw.setAnswer("0.");
}
}).start();
e.consume();
}
}

复制代码

public class MyCalculator {
public static void main(String[] args) {
// TODO Auto-generated method stub
MyWindow w = new MyWindow();
MyActionListener mal = new MyActionListener(w);
MyKeyListener mkl = new MyKeyListener(w);
w.init(mkl, mal);
w.setVisible(true);
}
}

复制代码