将多个if-else语句转换为更具功能性

Question

How does one make an if else statement functional

boolean condition1;
boolean condition2;

final Object a = new Object();
final Object b = new Object();
final Object c = new Object();
final Object d = new Object();

if (condition1 && condition2) {
   return a;
}
else if (condition1 && !condition2) {
   return b;
}
else if (!condition1 && condition2) {
   return c;
}
else {
   return d;
}

I would like to know how can one refactor this type of conditional statements to be more functional, with no overhead in performance preferbly.

I was thinking of Mapping predicates to the object, would this be an approach?

Answer 1

I've added 2 more conditions to spice it up a bit. The if/else statements can get pretty in-depth, so you can use bit-wise to clarify things and merge the conditions. To me, this clarifies the code - cause it's one level deep, no matter how many conditions.

final int BIT_CONDITION_1 = 0x01;
final int BIT_CONDITION_2 = 0x02;
final int BIT_CONDITION_3 = 0x04;
final int BIT_CONDITION_4 = 0x08;


boolean condition1 = false;
boolean condition2 = false;
boolean condition3 = false;
boolean condition4 = false;

int mergedConditions = 0;
if (condition1)
    mergedConditions |= BIT_CONDITION_1;
if (condition2)
    mergedConditions |= BIT_CONDITION_2;
if (condition3)
    mergedConditions |= BIT_CONDITION_3;
if (condition4)
    mergedConditions |= BIT_CONDITION_4;
// continue as needed

// now you can check all conditions using the set bits.
switch(mergedConditions) {
    case 0:      // no bits set
        System.out.println("No bits set");
        break;
    case 1:
        System.out.println("Conditions set = 1");
        break;
    case 2:
        System.out.println("Conditions set = 2");
        break;
    // You can also clarify case statements by using constants
    case (BIT_CONDITION_1 | BIT_CONDITION_2):
        System.out.println("Conditions set = 1,2");
        break;
    case 4:
        System.out.println("Conditions set = 3");
        break;
    case 5:
        System.out.println("Conditions set = 1,3");
        break;
    case 6:
        System.out.println("Conditions set = 2,3");
        break;
    case 7:
        System.out.println("Conditions set = 1,2,3");
        break;
    case 8:
        System.out.println("Conditions set = 4");
        break;
    case 9:
        System.out.println("Conditions set = 1,4");
        break;
    case 10:
        System.out.println("Conditions set = 2,4");
        break;
    case 11:
        System.out.println("Conditions set = 1,2,4");
        break;
    // etc ... Continue as needed
        }

Answer 2

For two conditions there's nothing wrong with your if/then/else statements. If you have more conditions, there's a way to "simplify" the code using a truth table.

public Object method()
{
    Object objects[] = { a, b, c, d }; // Assuming objects a, b, c and d exist...

    boolean condition1;
    boolean condition2;

    /* 
     * Truth Table
     * 
     *    condtion1  condition2   Object
     *      false      false        d
     *      false      true         c
     *      true       false        b
     *      true       true         a 
     */

    int selector = (condition1 ? 0 : 1) + (condition2 ? 0 : 2);

    return objects[selector];
}

Not sure if this is what you had in mind but it's a typical way to dispatch multiple conditions. While at first glance it looks arcane, if you document the entire truth table for all conditions it can be very safe, since it forces you to consider ALL possible combinations. This can really help when you have more than two conditions.