LAST UPDATE: MARCH 6, 2015

 

Some of these might be found in other library classes such as Arrays (if you find a more efficient implementation feel free to share it)

 

Feel free to leave constructive feedback (on the code/comments) / suggest methods.

package org.bjornkrols.utilities.array;

import java.util.Comparator;
import java.util.Random;

import org.bjornkrols.algorithms.sequence_search.BinarySearch;

/**
 * A set of utility methods for arrays.
 * 
 * @author 		Bjorn Krols (Botre)
 * @version		0.0
 * @since		March 6, 2015
 */

public final class ArrayUtilities {

	private ArrayUtilities() {
		// This class should never be instantiated.
		// Do not delete or make accessible.
	}
	
	private static final Random RANDOM = new Random();
		
	/**
	 * @return A string representation of the array with the following format: [0, 1, 2, ..., length - 1].
	 */
	public static String toString(Object[] array) {
		if (array == null) {
			return "null";
		}
		int max = array.length - 1;
		if (max == -1) {
			return "[]";
		}
		StringBuilder sb = new StringBuilder();
		sb.append('[');
		for (int i = 0; ; i++) {
			sb.append(array[i]);
			if (i == max) {
				return sb.append(']').toString();
			}
			sb.append(", ");
		}
	}
	
	/**
	 * Calls java.io.PrintStream.println on every entry of the array.
	 */
	public static void printlnContents(Object[] array) {
        if (array == null) {
        	System.out.println("null");
        	return;
        }
		for (int i = 0; i < array.length; i++) {
        	System.out.println(array[i]);
        }
    }
	
	/**
	 * Prints a String representation of the array and terminates the line.
	 */
	public static void printlnString(Object[] array) {
		System.out.println(toString(array));
	}

	/**
	 * @return A new array resulting from the concatenation of a set of arrays.
	 */
	public static int[] concatenate (int[]... arrays) {
		int size = 0;
		for (int[] array : arrays) size += array.length;
		int[] result = new int[size];
		int index = 0;
		for (int[] array : arrays) for (int element : array) result[index++] = element;	        
		return result;
	}

	/**
	 * @see ArrayUtilities#concatenate(int[]...)
	 */
	public static Object[] concatenate (Object[]... arrays) {
		int size = 0;
		for (Object[] array : arrays) size += array.length;
		Object[] result = new Object[size];
		int index = 0;
		for (Object[] array : arrays) for (Object element : array) result[index++] = element;	        
		return result;
	}
	
	/**
	 * Swaps the entries at indexes a & b.
	 */
	public static void swapEntriesByIndex(boolean[] array, int a, int b) {
		boolean temp = array[a];
		array[a] = array[b];
		array[b] = temp;
	}
	
	/**
	 * @see ArrayUtilities#swapEntriesByIndex(boolean[], int, int)
	 */
	public static void swapEntriesByIndex(byte[] array, int a, int b) {
		byte temp = array[a];
		array[a] = array[b];
		array[b] = temp;
	}
	
	/**
	 * @see ArrayUtilities#swapEntriesByIndex(boolean[], int, int)
	 */
	public static void swapEntriesByIndex(short[] array, int a, int b) {
		short temp = array[a];
		array[a] = array[b];
		array[b] = temp;
	}
	
	/**
	 * @see ArrayUtilities#swapEntriesByIndex(boolean[], int, int)
	 */
	public static void swapEntriesByIndex(char[] array, int a, int b) {
		char temp = array[a];
		array[a] = array[b];
		array[b] = temp;
	}
	
	/**
	 * @see ArrayUtilities#swapEntriesByIndex(boolean[], int, int)
	 */
	public static void swapEntriesByIndex(int[] array, int a, int b) {
		int temp = array[a];
		array[a] = array[b];
		array[b] = temp;
	}
	
	/**
	 * @see ArrayUtilities#swapEntriesByIndex(boolean[], int, int)
	 */
	public static void swapEntriesByIndex(long[] array, int a, int b) {
		long temp = array[a];
		array[a] = array[b];
		array[b] = temp;
	}
	
	/**
	 * @see ArrayUtilities#swapEntriesByIndex(boolean[], int, int)
	 */
	public static void swapEntriesByIndex(float[] array, int a, int b) {
		float temp = array[a];
		array[a] = array[b];
		array[b] = temp;
	}
	
	/**
	 * @see ArrayUtilities#swapEntriesByIndex(boolean[], int, int)
	 */
	public static void swapEntriesByIndex(double[] array, int a, int b) {
		double temp = array[a];
		array[a] = array[b];
		array[b] = temp;
	}
	
	/**
	 * @see ArrayUtilities#swapEntriesByIndex(boolean[], int, int)
	 */
	public static void swapEntriesByIndex(Object[] array, int a, int b) {
		Object temp = array[a];
		array[a] = array[b];
		array[b] = temp;
	}
	
	/**
	 * @return Whether the array is sorted.
	 */
	@SuppressWarnings("rawtypes")
	public static boolean isSorted(Comparable[] array) {
		return isSorted(array, 0, array.length - 1);
	}

	/**
	 * @return Whether the array is sorted between indexes low and high.
	 */
	@SuppressWarnings({ "rawtypes", "unchecked" })
	public static boolean isSorted(Comparable[] array, int low, int high) {
		for (int i = low + 1; i <= high; i++) if (array[i].compareTo(array[i - 1]) < 0) return false;
		return true;
	}
		
	/**
	 * @see ArrayUtilities#isSorted(Comparable[])
	 */
	@SuppressWarnings("rawtypes")
	public static boolean isSorted(Object[] array, Comparator comparator) {
		return isSorted(array, comparator, 0, array.length - 1);
	}
	
	/**
	 * @see ArrayUtilities#isSorted(Comparable[], int, int)
	 */
	@SuppressWarnings({ "rawtypes", "unchecked" })
	public static boolean isSorted(Object[] array, Comparator comparator, int low, int high) {
		for (int i = low + 1; i <= high; i++) if (comparator.compare(array[i], array[i - 1]) < 0) return false;
		return true;
	}
	
	/**
	 * @return Whether the sorted array contains a specific key value.
	 */
	public static boolean sortedContains(int[] array, int key) {
		return BinarySearch.getIndex(array, key) != -1;
	}
	
	/**
	 * Reverses the array.
	 */
	public static void reverse(int[] array) {
		int length = array.length;
	    for (int i = 0; i < length / 2; i++) {
	        array[i] = array[i] ^ array[length - i  - 1];
	        array[length - i  - 1] = array[i] ^ array[length - i  - 1];
	        array[i] = array[i] ^ array[length - i  - 1];
	    }
	}
	
	/**
	 * @return A random entry from the array.
	 */
	public static int getRandomEntry(int[] array) {
		return array[RANDOM.nextInt(array.length)];
	}
	
}

Edited March 6, 201510 yr by Botre

Updated

your reverse method

http://stackoverflow.com/questions/2137755/how-do-i-reverse-an-int-array-in-java

 

your concatenate method

http://stackoverflow.com/questions/80476/how-to-concatenate-two-arrays-in-java

 

at least give credit or post ref when you copy code m8

Edited March 6, 201510 yr by VladBots

your reverse method

http://stackoverflow.com/questions/2137755/how-do-i-reverse-an-int-array-in-java

 

your concatenate method

http://stackoverflow.com/questions/80476/how-to-concatenate-two-arrays-in-java

 

at least give credit or post ref when you copy code m8

 

The concatenate method is mine.

The reverse method not, who seriously credits stackoverflow code though ? Oo

The concatenate method is mine.

The reverse method not, who seriously credits stackoverflow code though ? Oo

it all looks the same except you changed the local var names lol owell

all code on stackoverflow is under the creative commons license