「java解析表达式」java解析表达式语法优先级
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本文目录一览：
JAVA 文本表达式解析成数学公式,计算出结果
正则表达分解字符串
然后运算
给你个例子。以前写的，现在忙没空给你写你这个了，public class CalStr { private String src;
/**
* constructor
*
* @param srcthe string(expression) to calculate
*/
public CalStr(String src) {
this.src = src;
}
/**
* calculate to get the result
*
* @return(double)result
*/
public double getResult() {
String postfix = getPostfix();
Stack stk = new Stack();
// System.out.println(postfix);
String parts[] = postfix.split( " + ");
double result = 0;
for (int i = 0; i parts.length; i++) {
char tmp = parts[i].charAt(0);
if (!isOperator(tmp)) {
stk.push(parts[i]);
} else {
double a = Double.parseDouble((String) stk.pop());
double b = Double.parseDouble((String) stk.pop());
// b is followed by a in the orignal expression
result = calculate(b, a, tmp);
stk.push(String.valueOf(result));
}
}
return result;
}
/**
* test if the character is an operator,such +,-,*,/
*
* @param opthe character to test
* @returntrue if op is an operator otherwise false
*/
private boolean isOperator(char op) {
return (op == '+ ' || op == '- ' || op == '* ' || op == '/ ');
}
/**
* calculate an expression such (a op b)
*
* @param anumber 1
* @param bnumber 2
* @param opthe operator
* @return(double)(a op b)
*/
public double calculate(double a, double b, char op) {
switch (op) {
case '+ ':
return a + b;
case '- ':
return a - b;
case '* ':
return a * b;
case '/ ':
return a / b;
}
return -1;
}
/**
* convert the suffix to postfix
*
* @returnthe postfix as a string
*/
private String getPostfix() {
Stack stk = new Stack();
String postfix = new String();
char op;
int i = 0;
while (i src.length()) {
if (Character.isDigit(src.charAt(i)) || src.charAt(i) == '. ') {
postfix += " ";
do {
postfix += src.charAt(i++);
} while ((i src.length())
(Character.isDigit(src.charAt(i))));
postfix += " ";
}
else {
switch (op = src.charAt(i++)) {
case '( ':
stk.push( "( ");
break;
case ') ':
while (stk.peek() != "( ") {
String tmp = (String) stk.pop();
postfix += tmp;
if (tmp.length() == 1 isOperator(tmp.charAt(0)))
postfix += " ";
}
stk.pop();
postfix += " ";
break;
case '+ ':
case '- ':
while ((!stk.empty()) (stk.peek() != "( ")) {
postfix += stk.pop() + " ";
}
stk.push(String.valueOf(new Character(op)));
break;
case '* ':
case '/ ':
while ((!stk.empty())
((stk.peek() == "* ") || (stk.peek() == "/ "))) {
postfix += stk.pop() + " ";
}
stk.push(String.valueOf(new Character(op)));
break;
}
}
}
ListIterator it = stk.listIterator(stk.size());
while (it.hasPrevious())
postfix += it.previous() + " ";
return postfix.trim().replaceAll( " +\\. ", ". ");
}
/**
* main function
*
* @param args
*/
public static void main(String args[]) {
System.out.println(new CalStr( "((1.5+6.000)*9+9.36)*(8+9-8*8+8*7) ")
.getResult());
}
}
java正则表达式解析Mysql数据库错误日志
System.out.println( new ReadSingleLineNumber().test2());
}
MySqlLog test2(){
String log = "2018-03-21T13:46:01.185376Z 0 [Warning] TIMESTAMP with implicit DEFAULT value is deprecated. Please use --explicit_defaults_for_timestamp server option (see documentation for more details).";
String[] head = log.substring(0, log.indexOf(']') + 1).split(" ");
return new MySqlLog(head[0].trim(), Integer.parseInt(head[1].trim()), head[2].trim().substring(head[2].trim().indexOf('[') + 1, head[2].trim().indexOf(']')), log.substring(log.indexOf(']') + 2).trim());
}
class MySqlLog{
String time;
int index;
String level;
String msg;
public MySqlLog(String time, int index, String level, String msg) {
this.time = time;
java解析字符串 算术表达式求值
Java 有一个jar包 叫 groovy
groovy可以实现动态执行 String格式的算数表达式
public static void main(String[] args) throws Exception{
String str1 = "1 + 2 * 3"; //表达式1 固定表达式
GroovyShell groovyShell = new GroovyShell();
Object value = groovyShell.evaluate(str1);
System.out.println(value);
String str2 = "A + B * C"; //表达式2 动态表达式
Binding binding = new Binding();
binding.setVariable("A",1); //表达式中 所有的A替换为1
binding.setVariable("B",2);//表达式中 所有的B替换为2
binding.setVariable("C",3);//表达式中 所有的C替换为3
GroovyShell groovyShell2 = new GroovyShell(binding);
Object value2 = groovyShell2.evaluate(str2); //str2 实际表达式为 1 + 2 * 3
System.out.println(value2);
}
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发布于：2022-11-24，除非注明，否则均为原创文章，转载请注明出处。