词法分析器
先展示下效果，输入一段代码，可以把每个关键字、运算符、括号等分出来，并连同其所在预先编号的表中的编号打印出来。预先编号的表笔者称为单词种别码表，具体在代码中一看就知。
算法设计
开发环境
Windows10+记事本+JDK8
代码
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.util.*;
public class LexicalAnalysis{
//为设计界面准备
JFrame jFrame = new JFrame("词法分析");//窗口
JTextArea jTextAreaTop = new JTextArea(12, 60);//文本框，用于输入代码
JTextArea jTextAreaBottom1 = new JTextArea(12, 60);//文本框，用于显示分析结果
JButton button1 = new JButton("点我");//按钮，点击后进行词法分析
//存放单词种别码表
private TreeMap<String, String> wordsTable;
//存放分析结果，按照代码输入顺序分析词法，记录词法分析结果
ArrayList<String> resultsKey = new ArrayList<>();
ArrayList<String> resultsValue = new ArrayList<>();
public LexicalAnalysis(){
//空参构造函数
//完成对单词种别码表的初始化
wordsTable = new TreeMap<>();
wordsTable.put("main", "1");
wordsTable.put("int", "2");
wordsTable.put("char", "3");
wordsTable.put("if", "4");
wordsTable.put("else", "5");
wordsTable.put("for", "6");
wordsTable.put("while", "7");
wordsTable.put("id", "10");//标识符
wordsTable.put("digit", "20");//数字
wordsTable.put("=", "21");
wordsTable.put("+", "22");
wordsTable.put("-", "23");
wordsTable.put("*", "24");
wordsTable.put("/", "25");
wordsTable.put("(", "26");
wordsTable.put(")", "27");
wordsTable.put("[", "28");
wordsTable.put("]", "29");
wordsTable.put("{", "30");
wordsTable.put("}", "31");
wordsTable.put(",", "32");
wordsTable.put(":", "33");
wordsTable.put(";", "34");
wordsTable.put(">", "35");
wordsTable.put("<", "36");
wordsTable.put(">=", "37");
wordsTable.put("<=", "38");
wordsTable.put("==", "39");
wordsTable.put("!=", "40");
wordsTable.put("!", "666");
wordsTable.put("\0", "1000");
wordsTable.put("ERROR", "-1");
/*测试用
wordsTable.forEach((key, value)->{
System.out.println(key);
});
*/
}
//程序入口
public static void main(String[] args){
new LexicalAnalysis().init();
}
public void init(){
//************************完成界面设置************************
//box1放入文本框、按钮（用box2盛装）、文本框
jFrame.setSize(new Dimension(1120, 500));
//设置文本框自动换行
jTextAreaTop.setLineWrap(true);
jTextAreaBottom1.setLineWrap(true);
//设置滚动条
JScrollPane jsp1 = new JScrollPane(jTextAreaTop);
JScrollPane jsp2 = new JScrollPane(jTextAreaBottom1);
Box box1 = Box.createVerticalBox();
box1.add(jsp1);
//为了按钮不随输入文字移动，把按钮放在box2里，再把box2放入box1
Box box2 = new Box(BoxLayout.X_AXIS);
box2.add(button1);
box1.add(box2);
box1.add(jsp2);
jFrame.add(box1);
jFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
jFrame.pack();
jFrame.setVisible(true);
//************************完成界面设置************************
//先给button1绑定监听器，后续分析结果的显示就靠他了
button1.addActionListener(new MyListener());
}
//写一个button1的监听器
class MyListener implements ActionListener{
public void actionPerformed(ActionEvent event){
resultsKey.clear();
resultsValue.clear();
jTextAreaBottom1.setText("");
//把用户输入的代码拿过来，放入字符串strSrc
String strSrc = jTextAreaTop.getText();
//************************词法分析核心逻辑代码************************
for(int i = 0; i < strSrc.length(); i++){
char c = strSrc.charAt(i);
String tmp = "" + c;
//***（1）忽略空格、换行、制表符
if(Character.isWhitespace(c) || c=='\n'){ //空白：空格,\t,\r,\n
continue;
}
//***（2）以字母开头的，判断是关键字还是标识符
else if(Character.isLetter(c)){
int j = i + 1;
for(; j < strSrc.length(); j++){
char cc = strSrc.charAt(j);
if(Character.isDigit(cc) || Character.isLetter(cc)){
tmp += cc;
}else{
break;
}
}
i=j-1;
if(wordsTable.containsKey(tmp)){ //关键字
resultsKey.add(wordsTable.get(tmp));
resultsValue.add(tmp);
}else{ //标识符
resultsKey.add(wordsTable.get("id"));
resultsValue.add(tmp);
}
}
//****（3）以数字开头的，就拼数
else if(Character.isDigit(c)){
int j = i + 1;
for(; j < strSrc.length(); j++){
char cc = strSrc.charAt(j);
//如果以数字开头，并且包含字母，报告编译出错
if(Character.isLetter(cc)){
System.out.println("标识符不能以数字开头，编译出错");
System.exit(-1);//强制非正常退出
}
if(Character.isDigit(cc)){
tmp += cc;
}else{
break;
}
}
i=j-1;
resultsKey.add(wordsTable.get("digit"));
resultsValue.add(tmp);
}
//***（4）判断特殊的>=,<=,==,!=
else if(wordsTable.containsKey(c + "")){
if(i + 1 < strSrc.length() && strSrc.charAt(i + 1) == '='){
tmp += strSrc.charAt(i + 1);
resultsKey.add(wordsTable.get(tmp));
resultsValue.add(tmp);
i++;
}
else{
resultsKey.add(wordsTable.get(tmp));
resultsValue.add(tmp);
}
}
else{
System.out.println("存在非法字符" + c);
System.exit(-1);//强制非正常退出
}
}
//把分析好的结果写入下面的文本框
for(int k = 0; k < resultsKey.size(); k++){
jTextAreaBottom1.append("(" + resultsKey.get(k) + ", " + resultsValue.get(k) + ")\n");
//System.out.print("(" + resultsKey.get(k) + ", " + resultsValue.get(k) + ")");
}
}
}
}
说明
笔者仅仅对如下关键单词进行了识别：
!
!=
(
)
*
+
,
-
/
:
;
<
<=
=
==
>
>=
ERROR
[
]
char
digit
else
for
id
if
int
main
while
{
}