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我目前正在研究旨在将字符串解析为链接列表的代码，并使用该列表作为计算操作的手段。如图所示，我将操作字符串当前设置为“1 + 2”，运行时返回整数 0。

非常感谢所有帮助。

import java.awt.Dimension;
import java.util.LinkedList;
import java.util.List;


public class LinkedListCalculator {

static List<String> CalcInput = new LinkedList<String>();
static String operation = "1+2";
static int equationLength = operation.length();
static int result = 0;
static int num = 0;
static int mul = 1;
static int finalNum = 0;
static char lastOperator = 0;


public static void addToList() {
    String finalNumString;
    if (lastOperator == '+') {
        finalNumString = Integer.toString(finalNum);
        CalcInput.add(finalNumString);
        CalcInput.add("+");
    } else if (lastOperator == '-') {
        finalNumString = Integer.toString(finalNum);
        CalcInput.add(finalNumString);
        CalcInput.add("-");
    } else if (lastOperator == '*') {
        finalNumString = Integer.toString(finalNum);
        CalcInput.add(finalNumString);
        CalcInput.add("*");
    } else if (lastOperator == '/') {
        finalNumString = Integer.toString(finalNum);
        CalcInput.add(finalNumString);
        CalcInput.add("/");
    }
}

public static void computeList() {
    int size = CalcInput.size();
    String lastIndex = null;
    for (int i = 0; i > size; i++) {
        String currentIndex = CalcInput.get(i);
            if (i > 0) {
                lastIndex = CalcInput.get(i - 1);
            }

            if (currentIndex == "+") {
                int lastIndexInt = Integer.valueOf(lastIndex);
                result += lastIndexInt;
            }
            if (currentIndex == "-") {
                int lastIndexInt = Integer.valueOf(lastIndex);
                result -= lastIndexInt;
            }
            if (currentIndex == "*") {
                int lastIndexInt = Integer.valueOf(lastIndex);
                result *= lastIndexInt;
            }
            if (currentIndex == "/") {
                int lastIndexInt = Integer.valueOf(lastIndex);
                result /= lastIndexInt;
            }
    }

}

public static void main(String [] args) {
    for (int currEqnCharNdx = 0; currEqnCharNdx < equationLength ; currEqnCharNdx++) {
        char j = operation.charAt(currEqnCharNdx);

        if (j >= '0' && j <= '9') {
            num = j - '0';
            finalNum *= mul;
            finalNum += num;
            mul = 10;
        } else if (operation.charAt(currEqnCharNdx) == '+') {
            addToList();
            lastOperator = '+';
            mul = 1;
            finalNum = 0;
        } else if (operation.charAt(currEqnCharNdx) == '-') {
            addToList();
            lastOperator = '-';
            mul = 1;
            finalNum = 0;
        } else if (operation.charAt(currEqnCharNdx) == '*') {
            addToList();
            lastOperator = '*';
            mul = 1;
            finalNum = 0;
        } else if (operation.charAt(currEqnCharNdx) == '/') {
            addToList();
            lastOperator = '/';
            mul = 1;
            finalNum = 0;
        } 
    }
    int i = CalcInput.size();
    computeList();
    System.out.println("result: " + result);
}
}
4

1 回答 1

0

你的代码有很多问题。以下是一些指向错误的指针：

String lastIndex = null;
    for (int i = 0; i > size; i++) {

这永远不会执行（更改为 i < size）

我也怀疑 addToList() 应该在设置 lastOperator 之后发生，等等。

 else if (operation.charAt(currEqnCharNdx) == '+') {
                addToList();
                lastOperator = '+';
                mul = 1;
                finalNum = 0;
            }

此外，这里（在 addToList() 中）：

if (lastOperator == '+') {
        finalNumString = Integer.toString(finalNum);
        CalcInput.add(finalNumString);
        CalcInput.add("+");
    }

你添加最后一个数字，加上 + 号，但是没有任何东西会导致添加 2，所以当它在最后总结时（如果你修复了我提到的其他事情）它会总结 1+，结果为 1 （而不是 1+2 做 3）。

这是它输出 1 的代码（请参见上面的最后一点）以供 OP 重现：

import java.awt.Dimension;
import java.util.LinkedList;
import java.util.List;
import java.util.StringTokenizer;


public class LinkedListCalculator {

static List<String> CalcInput = new LinkedList<String>();
static String operation = "1+2";
static int equationLength = operation.length();
static int result = 0;
static int num = 0;
static int mul = 1;
static int finalNum = 0;
static char lastOperator = 0;


public static void addToList() {
    String finalNumString;
    if (lastOperator == '+') {
        finalNumString = Integer.toString(finalNum);
        CalcInput.add(finalNumString);
        CalcInput.add("+");
    } else if (lastOperator == '-') {
        finalNumString = Integer.toString(finalNum);
        CalcInput.add(finalNumString);
        CalcInput.add("-");
    } else if (lastOperator == '*') {
        finalNumString = Integer.toString(finalNum);
        CalcInput.add(finalNumString);
        CalcInput.add("*");
    } else if (lastOperator == '/') {
        finalNumString = Integer.toString(finalNum);
        CalcInput.add(finalNumString);
        CalcInput.add("/");
    }
}

public static void computeList() {
    int size = CalcInput.size();
    String lastIndex = null;
    for (int i = 0; i < size; i++) {
        String currentIndex = CalcInput.get(i);
            if (i > 0) {
                lastIndex = CalcInput.get(i - 1);
            }

            if (currentIndex == "+") {
                int lastIndexInt = Integer.valueOf(lastIndex);
                result += lastIndexInt;
            }
            if (currentIndex == "-") {
                int lastIndexInt = Integer.valueOf(lastIndex);
                result -= lastIndexInt;
            }
            if (currentIndex == "*") {
                int lastIndexInt = Integer.valueOf(lastIndex);
                result *= lastIndexInt;
            }
            if (currentIndex == "/") {
                int lastIndexInt = Integer.valueOf(lastIndex);
                result /= lastIndexInt;
            }
    }

}

public static void main(String [] args) {



    for (int currEqnCharNdx = 0; currEqnCharNdx < equationLength ; currEqnCharNdx++) {
        char j = operation.charAt(currEqnCharNdx);

        if (j >= '0' && j <= '9') {
            num = j - '0';
            finalNum *= mul;
            finalNum += num;
            mul = 10;
        } else if (operation.charAt(currEqnCharNdx) == '+') {

            lastOperator = '+';
            addToList();
            mul = 1;
            finalNum = 0;
        } else if (operation.charAt(currEqnCharNdx) == '-') {
            addToList();
            lastOperator = '-';
            mul = 1;
            finalNum = 0;
        } else if (operation.charAt(currEqnCharNdx) == '*') {
            addToList();
            lastOperator = '*';
            mul = 1;
            finalNum = 0;
        } else if (operation.charAt(currEqnCharNdx) == '/') {
            addToList();
            lastOperator = '/';
            mul = 1;
            finalNum = 0;
        } 
    }
    int i = CalcInput.size();
    computeList();
    System.out.println("result: " + result);
}
}
于 2013-10-28T15:52:37.487 回答