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import java.util.HashMap;
import java.util.Map;
public abstract class Operator {
/**
* 运算符
*/
private char operator;
/**
* 运算符的优先级别,数字越大,优先级别越高
*/
private int priority;
private static Map<Character, Operator> operators = new HashMap<Character, Operator>();
private Operator(char operator, int priority) {
setOperator(operator);
setPriority(priority);
register(this);
}
private void register(Operator operator) {
operators.put(operator.getOperator(), operator);
}
/**
* 加法运算
*/
public final static Operator ADITION = new Operator('+', 100) {
public double eval(double left, double right) {
return left + right;
}
};
/**
* 减法运算
*/
public final static Operator SUBTRATION = new Operator('-', 100) {
public double eval(double left, double right) {
return left - right;
}
};
/**
* 乘法运算
*/
public final static Operator MULTIPLICATION = new Operator('*', 200) {
public double eval(double left, double right) {
return left * right;
}
};
/**
* 除法运算
*/
public final static Operator DIVITION = new Operator('/', 200) {
public double eval(double left, double right) {
return left / right;
}
};
/**
* 冪运算
*/
public final static Operator EXPONENT = new Operator('^', 300) {
public double eval(double left, double right) {
return Math.pow(left, right);
}
};
/**
* 取模运算
*/
public final static Operator MOD = new Operator('%', 200) {
public double eval(double left, double right) {
return left % right;
}
};
public char getOperator() {
return operator;
}
private void setOperator(char operator) {
this.operator = operator;
}
public int getPriority() {
return priority;
}
private void setPriority(int priority) {
this.priority = priority;
}
/**
* 根据某个运算符获得该运算符的优先级别
* @param c
* @return 运算符的优先级别
*/
public static int getPrority(char c) {
Operator op = operators.get(c);
if(op != null) {
return op.getPriority();
}
return 0;
}
/**
* 工具方法,判断某个字符是否是运算符
* @param c
* @return 是运算符返回 true,否则返回 false
*/
public static boolean isOperator(char c) {
return getInstance(c) != null;
}
public static boolean isOperator(String str) {
if(str.length() > 1) {
return false;
}
return isOperator(str.charAt(0));
}
/**
* 根据运算符获得 Operator 实例
* @param c
* @return 从注册中的 Operator 返回实例,尚未注册返回 null
*/
public static Operator getInstance(char c) {
return operators.get(c);
}
public static Operator getInstance(String str) {
if(str.length() > 1) {
return null;
}
return getInstance(str.charAt(0));
}
/**
* 根据操作数进行计算
* @param left 左操作数
* @param right 右操作数
* @return 计算结果
*/
public abstract double eval(double left, double right);
}
public class Test {
public static void main(String[] args) {
String str = "40944.0501-3.2*100";
Calculator cal = new Calculator();
double d = cal.eval(str);
System.out.println(d);
}
}
public interface MathSymbol {
/**
* 左括号
*/
public final static char LEFT_BRACKET = '(';
/**
* 右括号
*/
public final static char RIGHT_BRACKET = ')';
/**
* 中缀表达式中的空格,需要要忽略
*/
public final static char BLANK = ' ';
/**
* 小数点符号
*/
public final static char DECIMAL_POINT = '.';
/**
* 负号
*/
public final static char NEGATIVE_SIGN = '-';
/**
* 正号
*/
public final static char POSITIVE_SIGN = '+';
/**
* 后缀表达式的各段的分隔符
*/
public final static char SEPARATOR = ' ';
}
import java.util.Stack;
public class Calculator implements MathSymbol {
/**
* 计算中缀表达式
* @param expression
* @return
*/
public double eval(String expression) {
String str = infix2Suffix(expression);
//System.out.println(" Infix Expression: " + expression);
//System.out.println("Suffix Expression: " + str);
if(str == null) {
throw new IllegalArgumentException("Expression is null!");
}
String[] strs = str.split("\\s+");
Stack<String> stack = new Stack<String>();
for(int i = 0; i < strs.length; i++) {
if(!Operator.isOperator(strs[i])) {
stack.push(strs[i]);
} else {
Operator op = Operator.getInstance(strs[i]);
double right = Double.parseDouble(stack.pop());
double left = Double.parseDouble(stack.pop());
double result = op.eval(left, right);
stack.push(String.valueOf(result));
}
}
return Double.parseDouble(stack.pop());
}
/**
* 将中缀表达式转换为后缀表达式
* @param expression
* @return
*/
public String infix2Suffix(String expression) {
if(expression == null) {
return null;
}
char[] chs = expression.toCharArray();
Stack<Character> stack = new Stack<Character>();
StringBuilder sb = new StringBuilder(chs.length);
boolean appendSeparator = false;
boolean sign = true;
for(int i = 0; i < chs.length; i++) {
char c = chs[i];
if(c == BLANK) {
continue;
}
// Next line is used output stack information.
// System.out.printf("%-20s %s%n", stack, sb.toString());
if(appendSeparator) {
sb.append(SEPARATOR);
appendSeparator = false;
}
if(isSign(c) && sign) {
sb.append(c);
continue;
}
if(isNumber(c)) {
sign = false;
sb.append(c);
continue;
}
if(isLeftBracket(c)) {
stack.push(c);
continue;
}
if(isRightBracket(c)) {
sign = false;
while(stack.peek() != LEFT_BRACKET) {
sb.append(SEPARATOR);
sb.append(stack.pop());
}
stack.pop();
continue;
}
appendSeparator = true;
if(Operator.isOperator(c)) {
sign = true;
if(stack.isEmpty() || stack.peek() == LEFT_BRACKET) {
stack.push(c);
continue;
}
int precedence = Operator.getPrority(c);
while(!stack.isEmpty() && Operator.getPrority(stack.peek()) >= precedence) {
sb.append(SEPARATOR);
sb.append(stack.pop());
}
stack.push(c);
}
}
while(!stack.isEmpty()) {
sb.append(SEPARATOR);
sb.append(stack.pop());
}
return sb.toString();
}
/**
* 判断某个字符是否是正号或者负号
* @param c
* @return
*/
private boolean isSign(char c) {
if(c == NEGATIVE_SIGN || c == POSITIVE_SIGN) {
return true;
}
return false;
}
/**
* 判断某个字符是否为数字或者小数点
* @param c
* @return
*/
private boolean isNumber(char c) {
if((c >= '0' && c <= '9') || c == DECIMAL_POINT) {
return true;
}
return false;
}
/**
* 判断某个字符是否为左括号
* @param c
* @return
*/
private boolean isLeftBracket(char c) {
return c == LEFT_BRACKET;
}
/**
* 判断某个字符是否为右括号
* @param c
* @return
*/
private boolean isRightBracket(char c) {
return c == RIGHT_BRACKET;
}
}