CODEWITHSUNDEEP
javaintegerbooleanlong-integerbit
user2803086
user2803086

Reputation: 163

Store true/false in Integer using the bits

Situation

What I'm trying to achieve is to store true/false represented as a bit in a Integer/Long. The problem is that I'm unable to solve if a certain bit is 1 or 0.

Code

public class Test
{
    private static long unlocked = 0;

    public static void main(String[] args)
    {
        setUnlocked(1);
        setUnlocked(2);
        setUnlocked(3);
        System.out.println(isUnlocked(2);
    }

    public static void setUnlocked(int id)
    {
        unlocked += Math.pow(2, id);
    }

    public static boolean isUnlocked(int id)
    {
        // ???
        return false;
    }

}

As in the test case above, it will result in the following bits sequence: 1110 = 14.

Edit

Second Question:

    public static void setUnlocked(int id)
    {
        unlocked |= 1 << id;
    }

To

    public static void setUnlocked(int id, boolean set)
    {

    }

That will give the option to set the bit to 0 or 1 at the given location.

But how can I achieve this?

Upvotes: 1

Views: 253

Answers (2)

Eran
Eran

Reputation: 393841

Use bitwise operators :

public static void setUnlocked(int id)
{
    unlocked |= 1L<<id; // set the id'th bit
}

public static boolean isUnlocked(int id)
{
    return (unlocked & (1L<<id)) != 0; // get the id'th bit
}

1<<id is the fastest way to compute 2^id.

bitwise OR (|) lets you set a bit in the int.

bitwise AND (&) lets you get the value of a bit (by clearing all the other bits and checking if the result is not 0).

EDIT :

public static void setUnlocked(int id, boolean set)
{
    if (set) {
        unlocked |= 1L<<id; // set the id'th bit
    } else {
        unlocked &= 0xffffffffffffffffL ^ (1L<<id); // clear the id'th bit
    }
}

Upvotes: 6

Durandal
Durandal

Reputation: 20059

A more flexible approach is to use a plain simple Set<Integer>:

static Set<Integer> unlocked = new HashSet<>();

public static void setUnlocked(int id) {
    unlocked.add(id);
}

public static boolean isUnlocked(int id) {
    return unlocked.contains(id);
}

This approach does not rely on id's to be in any particular range. For thread safety, synchronize on the Set if needed.

Upvotes: 1

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