JAVA - How to make custom array sorting

In some situation is necessary make own custom sorting function. For this reason use class java.util.Comparator. In this class instance you must override compare() function.

/* -- array - one item with small first letter */

String[] array = { "one", "Two", "Three", "Four", "Fight" };

/* -- regular sorting */

Arrays.sort( array );

System.out.println( Arrays.toString( array ) );

/* -- sorting with own sorting function (ignoring letter size) */

Arrays.sort( array, new Comparator() {
  @Override
  public int compare( String s1, String s2 ) {
    return( s1.compareToIgnoreCase( s2 ) );
  }    
});

System.out.println( Arrays.toString( array ) );

The output is:

[Fight, Four, Three, Two, one]
[Fight, Four, one, Three, Two]

First output row is regular sorting. Second row is our custom sorting function that ignores letter case size.

JAVA - How to sort array elements in descending order

For sorting array elements use class java.util.Arrays. This class contains static methods for work with arrays.

String[] array = { "One", "Two", "Three", "Four", "Fight" };

Arrays.sort( array, Collections.reverseOrder() );

System.out.println( Arrays.toString( array ) );

For descending sorting use comparator Collections.reverseOrder().

Output is:

[Two, Three, One, Four, Fight]

JAVA - How to create multidimensional array

/* -- declaration and initialization of multidimensional 2D array */

int[][] doubleArray = 
{
  { 1, 3, 5 },
  { 2, 4, 6 }
};

/* -- go through multidimensional array (by rows) */

for ( int iRow = 0; iRow < doubleArray.length; iRow++ ) {   
  int[] iArray = doubleArray[ iRow ];          

  System.out.println( Arrays.toString( iArray ) );     
} 

Output:

[1, 3, 5]
[2, 4, 6]

JAVA - How to go through an array

Several method:

Variant 1

String[] array = new String[3];

array[0] = "One";
array[1] = "Two";
array[2] = "Three";

for ( int i = 0; i < array.length; i++ )
  System.out.println( array[i] );

Output is:

One 
Two 
Three 

Variant 2

String[] array = new String[3];

array[0] = "One";
array[1] = "Two";
array[2] = "Three";

for ( String item : array )
  System.out.println( item );

NOTE: Every next loop is into item variable filled next array item.

JAVA - How to quickly list (all) array elements

For quickly list array elements use class java.util.Arrays. This class contains static methods for work with arrays.

String[] array = new String[3];

array[0] = "One";
array[1] = "Two";
array[2] = "Three";

System.out.println( Arrays.toString( array ) );

The output is:

[One, Two, Three]

JAVA - How to copy array values between arrays

For copy array values between two arrays use System.arraycopy():

String[] array = new String[3];  

array[0] = "One"; 
array[1] = "Two"; 
array[2] = "Three"; 

String[] array1 = { "1", "2", "3" };

System.arraycopy( array1, 1, array, 0, 2 );

for ( int i = 0; i < array.length; i++ ) System.out.println( array[i] ); 

In this example are copied values of array1 (first param) from index 1 (second param) into array (third param). First value is inserted into 0 index (fourth param), copied are two (fifth param) items.

The output is:

2 3 Three

JAVA - How to sort array elements

For sorting array elements use class java.util.Arrays. This class contains static methods for working with arrays.

String[] array = { "One", "Two", "Three", "Four", "Fight" };

Arrays.sort( array );

System.out.println( Arrays.toString( array ) );

The output is:

[Fight, Four, One, Three, Two] 

NOTE: This is the most simplest variant of array sorting.

JAVA - How to create array

Exists several ways for creating java array.

Variant 1

/* creating */ 

String[] array = new String[3];

/* initialization */ 

array[0] = "One"; 
array[1] = "Two"; 
array[2] = "Three";

Variant 2

String[] array = { "one", "two", "three" };

NOTE: Arrays are indexed from zero [0]. When you use non-existed index is raised java.lang.ArrayIndexOutOfBoundsException exception.