Java, bit vectors

Question

I have to write a simple method that takes in an index and switches the "bit" at that index from 0 to 1 . I am having trouble writing the bitwise operators for this. I know it is simple but I can not get it. Below is what the method looks like. Thank you in advance!

/** 
 * 32-bit data initialized to all zeros. Here is what you will be using to represent
 * the Bit Vector.
 */

private int bits;

/** You may not add any more fields to this class other than the given one. */

/**
 * Sets the bit (sets to 1) pointed to by index.
 * @param index index of which bit to set.
 *        0 for the least significant bit (right most bit).
 *        31 for the most significant bit.
 */
public void set(int index)
{
            //It is here where I can not figure it out. Thank you!
    System.out.println(~bits);
    System.out.println("setting bit: " + bits + " to: " + index);
}

Answer 1

You should use a BitSet . If you want to do this yourself you can say:

public void set(int index) { 
    bits |= (1 << index);
}

If this is homework, and the above code looks like magic, you really need to read up on bitwise operators.

This code can be interpreted as:

• Start with the number 1, and move all of its bits over index number of times.
• Set the value of bits equal to the value of bits OR 'ed with the value from the previous step