四则运算（基于控制台）

public TreeNode createTree(String expression) {
		/*
		 * 去除表达式首部和尾部的多余括号 当出现了括号不匹配时出现异常 抛出
		 */
		if (expression.indexOf("(") == 0) {
			for (int i = 0; i < expression.length(); i++) {
				if (expression.startsWith("(") == true) {
					if (expression.endsWith(")") == true) {
						expression = expression.substring(1,
								expression.length() - 1);
					} else {
						/*
						 * 抛出异常 括号不比配
						 */
					}

				}
			}
		}
		char[] exp = expression.toCharArray();

		TreeNode newNode = new TreeNode();
		String leftString = new String();
		String rightString = new String();
		String stack = new String(); // 用于存储括号的栈 当表达式检测完毕后 若栈不为空 这说明括号使用不合法
		if (checkOperator(expression) == true) {
			int index = 0; // 记录最先扫描到的不在括号中的加号或减号 必为表达式运算的最后一次操作
			int multi_div = 0; // 记录最先扫描到的不在括号中的乘号或除号的位置 只有在扫描不到加号和减号的前提下才有用
			for (int i = exp.length - 1; i >= 0; i--) {
				if (exp[i] == ‘)‘) {
					stack = stack + exp[i];
				} else if (exp[i] == ‘(‘) {
					if (stack.length() > 0) {
						stack = stack.substring(0, stack.length() - 1);
					}
				} else if (exp[i] == ‘+‘ && stack.length() == 0
						|| exp[i] == ‘-‘ && stack.length() == 0) {
					index = i;
					break;
				} else if (exp[i] == ‘/‘ && stack.length() == 0
						|| exp[i] == ‘*‘ && stack.length() == 0) {
					multi_div = i;
				} else {
					if (exp[i] < 48 || exp[i] > 57) {
						/*
						 * 抛出异常 出现不合法的字符
						 */
					}
				}
			}
			if (stack.length() != 0) {
				/*
				 * 抛出异常 括号不匹配
				 */
			}
			int separator;
			if (index != 0) { // 说明表达式的最后运算的为加法或减法
				separator = index;
			} else {
				separator = multi_div;
			}
			newNode.data = String.valueOf(exp[separator]);
			int pos = 0;
			for (; pos < separator; pos++) {
				leftString = leftString + exp[pos];
			}
			pos++;
			for (; pos < exp.length; pos++) {
				rightString = rightString + exp[pos];
			}
			if (node == null) {
				node = newNode;
			}
			newNode.left = createTree(leftString);
			newNode.right = createTree(rightString);
		} else {

			newNode.data = expression;

		}
		return newNode;
	}