测试代码：
码云链接
import java.util.Scanner;
public class MyDCTester {
public static void main(String[] args) {
String expression, again;
int result;
try {
Scanner in = new Scanner(System.in);
do {
MyDC evaluator = new MyDC();
System.out.println("Enter a valid postfix expression: ");
expression = in.nextLine();
result = evaluator.evaluate(expression);
System.out.println();
System.out.println("That expression equals " + result);
System.out.print("Evaluate another expression [Y/N]? ");
again = in.nextLine();
System.out.println();
}
while (again.equalsIgnoreCase("y"));
} catch (Exception IOException) {
System.out.println("Input exception reported");
}
}
}
补充代码：
码云链接
import java.util.StringTokenizer;
import java.util.Stack;
public class MyDC {
private final char ADD = '+';
private final char SUBTRACT = '-';
private final char MULTIPLY = '*';
private final char DIVIDE = '/';
private Stack stack;
public MyDC() {
stack = new Stack<Integer>();
}
public int evaluate(String expr) {
int op1, op2, result = 0;
String token;
StringTokenizer tokenizer = new StringTokenizer(expr);
while (tokenizer.hasMoreTokens()) {
token = tokenizer.nextToken();
if (isOperator(token))//如果是操作数
{
op2 = (stack.pop()).intValue();
op1 = (stack.pop()).intValue();
result = evalSingleOp(token.charAt(0), op1, op2);
stack.push(new Integer(result));
} else
stack.push(new Integer(Integer.parseInt(token)));
}
return result;
}
private boolean isOperator(String token) {
return (token.equals("+") || token.equals("-") || token.equals("*") || token.equals("/"));
}
private int evalSingleOp(char operation, int op1, int op2) {
int result = 0;
switch (operation) {
case ADD:
result = op1 + op2;
break;
case SUBTRACT:
result = op1 - op2;
break;
case MULTIPLY:
result = op1 * op2;
break;
case DIVIDE:
result = op1 / op2;
}
return result;
}
}
测试截图（加水印）：