Java Programming One and Multidimensional Arrays

How to define array in java?

  • An array is a group of same type of variables that are referred to by a common name.
  • Arrays can be created for any type and may have one or more dimensions.
  • Specific element in array can be accessed by its index.

What is One Dimensional Arrays?

  • A one dimensional array is a list of like-typed variables.
  • syntax:
    type array_var[];
    
    In above syntax, type declares the base type of the array. what type of data the array will hold.
    int employee_id[];
    
    In above code, employee_id is the array variable, but here no array will be created, only null is set to employee_id(An array with no value).
  • new keyword must be used to allocate memory for array variable. new is a special operator that allocates memory.
    array_var = new type[size];
    

    here type specifies the type of data being allocated, size specifies the number of elements in the array. array_var is the array variable that is linked to the variable.

    employee_id = new int[12];
    
    employee_id is the integer array which will have 12 integers. All elements in this array are initialized to 0.
    employee_id[2] = 1002;
    
    here 1002 value is assigned to 3rd element in the array since array index starts at 0. To print 3rd element in the array.
    System.out.println(employee_id[2]);
    
    Example:
    // Array one dimensional sample code.                                           
    class ArrayOneDimensionTest {                                                   
     public static void main(String args[]) {                                       
      // declares integer one dimensional array                                     
      int employee_id[];                                                            
                                                                                    
      // allocates memory for integer array which will have 5 elements.             
      employee_id = new int[5];                                                     
                                                                                    
      //initializes value to array indexes.                                         
      employee_id[0] = 1001;                                                        
      employee_id[1] = 1002;                                                        
      employee_id[2] = 1003;                                                        
      employee_id[3] = 1004;                                                        
      employee_id[4] = 1005;                                                        
      //prints 4th employee id in the employee_id array.                            
      System.out.println("4th Employee id is:" +   employee_id[3]);                 
     }                                                                              
    }  
    
    Output:
    4th Employee id is:1004
    
    We can also declare, allocate memory and length in the single line as below
    int employee_id = new int[5];
    
    Arrays can be initialized in declaration itself as below.
     int employee_id[] = {1001, 1002, 1003, 1004, 1005};
    
    integer array will be created with 5 elements and assigned employee_id array variable.
    Example:
    // Array one dimensional sample code.                                           
    class ArrayOneDimensionTest1 {                                                  
     public static void main(String args[]) {                                       
      // declares integer one dimensional array and initializes data                                   
      int employee_id[] = {1001, 1002, 1003, 1004, 1005};                           
                                                                                    
      //prints 4th employee id in the employee_id array.                            
      System.out.println("4th Employee id is:" +   employee_id[3]);                 
     }                                                                              
    }    
    
    Output:
    4th Employee id is:1004
    

    Is there any alternate way to declare array?

    type[] variable_name;
    
    Example:
    int a[] = new int[5];
    int[] a = new int[5];
    

Example to declare, initializes and print all elements in the one dimensional array in java:

// Array one dimensional sample code.                                           
class ArrayOneDimensionTest2 {                                                  
 public static void main(String args[]) {                                       
  // declares integer one dimensional array                                     
  int employee_id[] = {1001, 1002, 1003, 1004, 1005};                           
                                                                                
  //prints all employee id in the array.                                        
  for(int i=0; i<5; i++) {                                                      
   System.out.println("Employee id[" + i +"] is:" +   employee_id[i]);          
  }                                                                             
 }                                                                              
}   
Output:
Employee id[0] is:1001
Employee id[1] is:1002
Employee id[2] is:1003
Employee id[3] is:1004
Employee id[4] is:1005

How to define multidimensional arrays?

Multidimensional Arrays: are actually arrays of arrays.
  • Declaring a multidimensional array variable, we need to specify additional index using another set of square brackets([]).
  • Two dimensional array variable example:
    int matrix[][] = new int[5][5];
    //alternate way to declare and allocate memory and size.
    //int[][] matrix = new int[5][5];
    
    Two dimensional array matrix example:
    // Array two dimensional sample code.                                           
    class TwoDimensionalArrayTest {                                                 
     public static void main(String args[]) {                                       
      // declares two dimensional array and allocates memory and size               
      int matrix[][] = new int[3][5];                                               
                                                                                    
      int val = 0;                                                                  
      //initializes value in array of array elements.                               
      for(int i=0; i<3; i++) {                                                      
       for(int j=0; j<5; j++) {                                                     
        matrix[i][j] = val;                                                         
        val = val + 1;                                                              
       }                                                                            
      }                                                                             
                                                                                    
      //prints all elements in array of arrays                                      
      for(int i=0; i<3; i++) {                                                      
       for(int j=0; j<5; j++) {                                                     
        System.out.print(matrix[i][j] + " ");                                       
       }                                                                            
       System.out.println();                                                        
      }                                                                             
     }                                                                              
    }  
    
    Output:
    0 1 2 3 4 
    5 6 7 8 9 
    10 11 12 13 14
    
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