Java Arrays

An array is a type of object that contains values called elements. This gives you a convenient bag or holder for a group of values that can be moved around a program, and allows you to access and change values as you need them. Unlike variables which are accessed by a name, elements are accessed by numbers starting from zero.

Arrays in Java are similar in syntax to arrays in other languages such as C/C++ and Visual Basic.

On this page

Single Dimension Arrays

Declaration of array

The declaration of an array does not allocate any storage, it just announces the intention of creating an array.

Thus the following will cause a compile time error:

int num[5];

The size of an array is given when it is actually created with the new operator thus.

int num[]; //declartion

num = new int[5]; //allocation

int num[]=new int[5]; //initilization

num[0]=900; Assignment

System.out.println(num[0]); //printing array elements

Initilization of arrays

int items[]={23,232,455,667};

Also the square brackets can be placed either after the data type or after the name of the array. Thus both of the following are legal

int[] num;

int num[];

You can read these as either:
•An integer array named num
•An integer type in an array called num.

A big difference between Java and C/C++ is that Java arrays know how big they are, and the language provides protection from walking off the end of arrays.

int len=array_name.length;

Examples

Simple Single Dimension array example


public class ArrayDemo1
{
  public static void main(String[] args) 
  {
	 int values[]; //declaration
	 values=new int[3];

	 values[0]=1001;
	 values[1]=1002;
	 values[2]=1003;
 
	 System.out.println(values[0]);
	 System.out.println(values[1]);
	 System.out.println(values[2]);
  }
}

printing java Array elements using traditional for loop


public class ArrayDemo2
{
  public static void main(String[] args) 
  {
    int values[]={45,56,78,89,87,566,780,74,89,76};
  
   //finding the array size 
   int size=values.length;
   System.out.println("Array size is..."+size);
  
   for(int i=0;i<size;i++)
    {
     System.out.print(values[i]+"\t");
    }
  }
}

Printing java array elements using for-each loop (Since 1.5)


public class ArrayDemo3
{
  public static void main(String[] args) 
  {
   int values[]={45,56,78,89,87,566,780,74,89,555};

    for(int item:values)
      {
         System.out.println(item);
       }
  }
}

Multi Dimensional Arrays

An array declaration can have multiple sets of square brackets. Java does not formally support multi dimensional arrays, however it does support arrays of arrays, also known as nested arrays.

The important difference between multi dimensional arrays, as in C/C++ and nested arrays, is that each array does not have to be of the same length. If you think of an array as a matrix, the matrix does not have to be a rectangle.

Declaration of arrays

int items[4][5]; * //illegal

int items[][]; //declaration

Allocation

items=new int[][5]; //illegal

int items[][]; //declaration
items=new int[5][5]; //legal
items=new int[5][]; //legal
items[0]=new int[5]; // 0 th row with 5 columns
items[1]=new int[7]; // 1 st row with 7 columns

initilization of nested arrays


        String subjects[][]={
			{"asp","jsp","dsp"},
			{"c","c++","java","smalltalk"},
			{"bdps","aptech"}
	    };

Examples:

simple nested arrays example


public class NestedArrayDemo1 
{
  public static void main(String[] args) 
  {
    int values[][]; //declaration
    values=new int[2][2]; //allocation	 	
    values[0][0]=1001; values[0][1]=1002;	 	
    values[1][0]=2001;  values[1][1]=2002;	 	
   System.out.println(values[0][0]+"\t"+values[0][1]);
   System.out.println(values[1][0]+"\t"+values[1][1]);	 	
  }
}

printing nested array elements using traditional for loop


public class NestedArrayDemo2 
{
  public static void main(String[] args) 
  {
      String subjects[][]={
	 {"c","c++","java","small talk"},
	 {"html","xml","wml"},
	 {"asp","jsp"}
      };

   int rows=subjects.length; //finding rows
   for(int i=0;i<rows;i++)
    {
        int cols=subjects[i].length;
        System.out.println("Columns for "+i+" row is..."+cols);        
        for(int j=0;j<cols;j++)
         {
           System.out.print(subjects[i][j]+"\t"); 
         }
          System.out.println();
      }
   }
}

printing nested array elements using for-each loop (Since 1.5)


public class NestedArrayDemo3 
{
 public static void main(String[] args) 
 {
      String subjects[][]={
             {"c","c++","java","small talk"},
             {"html","xml","wml"},
             {"asp","jsp"}
          };
        for(String rows[]:subjects)
          {
              for(String cols:rows)
	 {
	  System.out.print(cols+"\t");	 
	 }
	 System.out.println();
            }
   }
}