Strategy Pattern

Lab Java Advanced 30 points

Write interface Operation (long apply(long a, long b)) and store implementations in a Map<String, Operation> for add, sub, mul, max. Read op a b lines and print the results or unknown op. Use anonymous classes (no lambdas yet).

Input

n, then n lines.

Output

n lines.

Example

Input

4
add 2 3
mul 4 5
max -1 -9
pow 2 3

Output

5
20
-1
unknown op

Sample input available Sample output available

Editor

Java

Hints

new Operation() { ... } creates an anonymous class implementing the interface.

Solution explanation

Choosing behaviour by looking up an object is the strategy pattern. Lambdas (chapter 21) make it shorter.

Show solution

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

interface Operation {
    long apply(long a, long b);
}

public class Main {
    public static void main(String[] args) {
        Map<String, Operation> ops = new HashMap<String, Operation>();
        ops.put("add", new Operation() {
            public long apply(long a, long b) { return a + b; }
        });
        ops.put("sub", new Operation() {
            public long apply(long a, long b) { return a - b; }
        });
        ops.put("mul", new Operation() {
            public long apply(long a, long b) { return a * b; }
        });
        ops.put("max", new Operation() {
            public long apply(long a, long b) { return Math.max(a, b); }
        });
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        for (int i = 0; i < n; i++) {
            String name = sc.next();
            long a = sc.nextLong(), b = sc.nextLong();
            Operation op = ops.get(name);
            System.out.println(op == null ? "unknown op" : String.valueOf(op.apply(a, b)));
        }
    }
}

Output

Answer