简单计算器

https://www.lintcode.com/problem/simple-calculator/description

import java.util.HashMap;
import java.util.Map;

public class Calculator {
    /**
     * @param a:        An integer
     * @param operator: A character, +, -, *, /.
     * @param b:        An integer
     * @return: The result
     */
    public int calculate(int a, char operator, int b) {
        // write your code here
        Map<Character, Operate> map = new HashMap<>();
        map.put('+', new Operate() {
            @Override
            public int operate(int x, int y) {
                return x + y;
            }
        });
        map.put('-', new Operate() {
            @Override
            public int operate(int x, int y) {
                return x - y;
            }
        });
        map.put('*', new Operate() {
            @Override
            public int operate(int x, int y) {
                return x * y;
            }
        });
        map.put('/', new Operate() {
            @Override
            public int operate(int x, int y) {
                return x / y;
            }
        });
        Operate operate = map.get(operator);
        return operate.operate(a, b);
    }

    private interface Operate {
        int operate(int x, int y);
    }
}