Java計算器是一種基于Java語言的計算器應用程序，可以實現基本的四則運算和復雜的科學計算。下面介紹Java計算器的流程圖和代碼。

流程圖如下：

+----------------+
|  輸入表達式    |
+----------------+
|
|
v
+----------------+
|  解析表達式    |
+----------------+
|
|
v
+----------------+
|   計算表達式   |
+----------------+
|
|
v
+----------------+
|   輸出結果     |
+----------------+

代碼如下：

import java.util.*;
public class Calculator {
// 解析表達式
public static ListparseExpression(String expression) {
Listtokens = new ArrayList();
int i = 0;
while (i< expression.length()) {
char c = expression.charAt(i);
if (c >= '0' && c<= '9' || c == '.') {
// 解析數字
int j = i + 1;
while (j< expression.length() && (expression.charAt(j) >= '0' && expression.charAt(j)<= '9' || expression.charAt(j) == '.')) {
j++;
}
tokens.add(expression.substring(i, j));
i = j;
} else if (c == '+' || c == '-' || c == '*' || c == '/') {
// 解析運算符
tokens.add(Character.toString(c));
i++;
} else {
// 不支持的字符
throw new IllegalArgumentException("Unsupported character: " + c);
}
}
return tokens;
}
// 計算表達式
public static double evaluateExpression(Listtokens) {
Stackstack = new Stack();
for (String token : tokens) {
if (token.equals("+")) {
double num2 = stack.pop();
double num1 = stack.pop();
stack.push(num1 + num2);
} else if (token.equals("-")) {
double num2 = stack.pop();
double num1 = stack.pop();
stack.push(num1 - num2);
} else if (token.equals("*")) {
double num2 = stack.pop();
double num1 = stack.pop();
stack.push(num1 * num2);
} else if (token.equals("/")) {
double num2 = stack.pop();
double num1 = stack.pop();
stack.push(num1 / num2);
} else {
double num = Double.parseDouble(token);
stack.push(num);
}
}
return stack.pop();
}
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
while (true) {
System.out.print("請輸入表達式：");
String expression = scanner.nextLine();
try {
Listtokens = parseExpression(expression);
double result = evaluateExpression(tokens);
System.out.println(expression + " = " + result);
} catch (IllegalArgumentException e) {
System.out.println("Error: " + e.getMessage());
}
}
}
}