Java


Java: Breakdown an integer to the powers of two it is composed from 1

The following function will accept an integer number as input and will produce an IntStream, which is a sequence of primitive int-valued elements that supports sequential and parallel aggregate operations.

public static IntStream splitToPowersOfTwo(final int input) {

    int temp = input;
    final IntStream.Builder builder = IntStream.builder();

    while (temp != 0) {

        //Integer.lowestOneBit: Finds the lowest-order ("rightmost") one-bit in the specified int value and returns an int number that has only the bit in the previously matched position set as 1. This value is a power of two that is one of the components of the number. If the number is zero, the function returns zero.
        final int powerOfTwo = Integer.lowestOneBit(temp);
        builder.add(powerOfTwo);
        //We update our temp by subtracting the number we got, our goal is to remove the previously matched bit and get the next one on the next iteration.
        temp = temp & ~ powerOfTwo;
    }

    return builder.build();
}

We used Integer.lowestOneBit as it makes it easy for us to breakdown the number to its power of two components by matching for us only one bit at time.

Example of usage:

Scenario: We want to breakdown an integer to the powers of two that their sum produces the number and create a String with those values. Using our function, we can do the following:

final String output = splitToPowersOfTwo(flags).mapToObj(Integer::toString).collect(Collectors.joining(", "));

Note: an IntStream is not the same as a Stream<Integer>, we used .mapToObj(Integer::toString) which calls the static method Integer.toString(int). This is different to calling .map(Integer::toString) on a Stream<Integer> as the latter won’t compile because it is ambiguous.

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Java: Given a path to a file, create the folders to it

Assuming you have a full path to a file you want to create but the folder to it might exist or not, you can use the following code in your program to check if the folder exists and if it doesn’t, create it.

//The file we want to create;
final String logFileName = "./someFolder/anotherFolder/etc/myFile.txt";
//We find the last occurrence of the File.separator value, which will allow us to separate the path from the filename
final int lastIndex = logFileName.lastIndexOf(File.separator);
//The actual path we want to make sure it exists
final String dirPath = logFileName.substring(0, lastIndex > 0 ? lastIndex : logFileName.length());
//We try to use the folder by assigning it to a File object
final File theDir = new File(dirPath);
//Make the check that the folder exists
if (!theDir.exists()) {
    //If the folder does not exist, create it
    theDir.mkdirs();
}
//Continue with execution