5+3*4的表达式树Java代码并将结果打印出来

下面是一个 Java 代码实现 5+3*4 表达式树的构建和计算过程，并将结果打印出来：

class TreeNode {
    char val;
    TreeNode left, right;

    TreeNode(char val) {
        this.val = val;
        this.left = this.right = null;
    }
}

public class ExpressionTree {
    public int evaluateExpressionTree(TreeNode root) {
        if (root == null) {
            return 0;
        }

        if (root.left == null && root.right == null) {
            return root.val - '0';
        }

        int leftSum = evaluateExpressionTree(root.left);
        int rightSum = evaluateExpressionTree(root.right);

        switch (root.val) {
            case '+':
                return leftSum + rightSum;
            case '-':
                return leftSum - rightSum;
            case '*':
                return leftSum * rightSum;
            case '/':
                return leftSum / rightSum;
            default:
                return 0;
        }
    }

    public TreeNode buildExpressionTree(char[] postfix) {
        Stack<TreeNode> stack = new Stack<>();
        int n = postfix.length;

        for (int i = 0; i < n; i++) {
            char c = postfix[i];
            if (isOperator(c)) {
                TreeNode node = new TreeNode(c);
                node.right = stack.pop();
                node.left = stack.pop();
                stack.push(node);
            } else {
                stack.push(new TreeNode(c));
            }
        }

        return stack.pop();
    }

    private boolean isOperator(char c) {
        return c == '+' || c == '-' || c == '*' || c == '/';
    }

    public static void main(String[] args) {
        ExpressionTree tree = new ExpressionTree();
        String postfix = "534*+";
        TreeNode root = tree.buildExpressionTree(postfix.toCharArray());
        int result = tree.evaluateExpressionTree(root);
        System.out.println(result);
    }
}

输出结果为 17，即 5 + 3 * 4 的计算结果。