This is my java implementation (O(n)) about how to calculate infix expression with no parenthesis. For example, when we input "3 + 4 * 4 / 8", we will get a double type answer is 5.0. Here to make the algorithm simple, we don't consider any parenthesis in the expression. Below is my code. I think my implementation is kind of tedious long. Can anyone give me some advice to make it more clean?

public double computeInfixExpr(String input) {
        String[] expr = input.split(" ");
        int i = 0;
        double operLeft = Integer.valueOf(expr[i++]);
        while (i < expr.length) {
            String operator = expr[i++];
            double operRight = Double.valueOf(expr[i++]);
            switch (operator) {
                case "*":
                    operLeft = operLeft * operRight;
                    break;
                case "/":
                    operLeft = operLeft / operRight;
                    break;
                case "+":
                    while (i < expr.length) {
                        String operator2 = expr[i++];
                        if (operator2.equals("+") || operator2.equals("-")) {
                            i--;
                            break;
                        }
                        if (operator2.equals("*")) {
                            operRight = operRight * Double.valueOf(expr[i++]);
                        }
                        if (operator2.equals("/")) {
                            operRight = operRight / Double.valueOf(expr[i++]);
                        }
                    }
                    operLeft = operLeft + operRight;
                    break;
                case "-":
                    while (i < expr.length) {
                        String operator2 = expr[i++];
                        if (operator2.equals("+") || operator2.equals("-")) {
                            i--;
                            break;
                        }
                        if (operator2.equals("*")) {
                            operRight = operRight * Double.valueOf(expr[i++]);
                        }
                        if (operator2.equals("/")) {
                            operRight = operRight / Double.valueOf(expr[i++]);
                        }
                    }
                    operLeft = operLeft - operRight;
                    break;
            }
        }
        return operLeft;
    }