实验截图
实验代码
import java.util.StringTokenizer;
import java.util.Stack;
public class MyDC {
/**
* constant for addition symbol
*/
private final char ADD = '+';
/**
* constant for subtraction symbol
*/
private final char SUBTRACT = '-';
/**
* constant for multiplication symbol
*/
private final char MULTIPLY = '*';
/**
* constant for division symbol
*/
private final char DIVIDE = '/';
/**
* the stack
*/
private Stack<Integer> 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();
//如果是运算符,调用isOperator
if (isOperator(token)) {
op2=(stack.pop()).intValue();//从栈中弹出操作数2
op1=(stack.pop()).intValue();//从栈中弹出操作数1
result=evalSingleOp(token.charAt(0),op1,op2);//根据运算符和两个操作数调用evalSingleOp计算result;
stack.push(new Integer(result));//计算result入栈;
} else//如果是操作数
stack.push(new Integer(Integer.parseInt(token)));//操作数入栈;
}
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;
}
}
练习总结
- 1、对于
isOperator()
的调用不够明确。
- 2、计算中间结果的代码为
result=evalSingleOp(token.charAt(0),op1,op2);
。
- 3、操作数入栈需进行强制类型转换
Integer.parseInt(token)
。