Arrays in Java

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Array in java represents a group of fixed homogeneous elements that can be referenced with same variable. Array elements storage is index based and follow the mechanism of contiguous memory location which states that 1st element will store at index 0, 2nd element will store at index 1, 3rd element will store at index 2 and so on.

Arrays Class Hierarchy:

java.lang.Object
java.util.Arrays

Arrays Class Syntax:

public class Arrays
extends Object

Important points

  • Array in java represents an object of a dynamically generated class.
  • Arrays class extends Object class.
  • Arrays in java represents object that’s why we can get length of an array using member length. In C/C++ sizeof operator is used to find the array length.
  • Array in java can be used as a static variable, a instance variable or a method parameter/argument.
  • Both primitive values or objects can be stored in Java array.
  • Both single and multi-dimensional array can be created in java.
  • The concept of anonymous array is also there in Java.
  • Array represents the group of fixed elements. We cannot change the array size. Collection framework can be used as dynamic size group of items.

Arrays Methods

Method Description
get(Object array, int index) It is used to get the value of the indexed component in the given array object.
getBoolean(Object array, int index) It is used to get the value of the indexed component in the given array object, as a boolean.
getByte(Object array, int index) It is used to get the value of the indexed component in the given array object, as a byte.
getChar(Object array, int index) It is used to get the value of the indexed component in the given array object, as a char.
getDouble(Object array, int index) It is used to get the value of the indexed component in the given array object, as a double.
getFloat(Object array, int index) It is used to get the value of the indexed component in the given array object, as a float.
getInt(Object array, int index) It is used to get the value of the indexed component in the given array object, as an int.
getLength(Object array) It is used to get the length of the given array object, as an int.
getLong(Object array, int index) It is used to get the value of the indexed component in the given array object, as a long.
getShort(Object array, int index) It is used to get the value of the indexed component in the given array object, as a short.
newInstance(Class<?> componentType, int… dimensions) It is used to create a new array with the given component type and dimensions.
newInstance(Class<?> componentType, int length) It is used to create a new array with the given component type and length.
set(Object array, int index, Object value) It is used to set the value of the indexed component of the given array object to the specified new value.
setBoolean(Object array, int index, boolean z) It is used to set the value of the indexed component of the given array object to the specified boolean value.
setByte(Object array, int index, byte b) It is used to set the value of the indexed component of the given array object to the specified byte value.
setChar(Object array, int index, char c) It is used to set the value of the indexed component of the given array object to the specified char value.
setDouble(Object array, int index, double d) It is used to set the value of the indexed component of the given array object to the specified double value.
setFloat(Object array, int index, float f) It is used to set the value of the indexed component of the given array object to the specified float value.
setInt(Object array, int index, int i) It is used to set the value of the indexed component of the given array object to the specified int value.
setLong(Object array, int index, long l) It is used to set the value of the indexed component of the given array object to the specified long value.
setShort(Object array, int index, short s) It is used to set the value of the indexed component of the given array object to the specified short value.

Single Dimensional Array

Syntax: Declare an Array

dataType[] arr;  

dataType []arr;

dataType arr[];

Syntax: Instantiate an Array

arrayReferenceVariable = new datatype[size];

Syntax: Insert elements to an Array

arrayReferenceVariable = {element1, element2, ..., elementn};

Example

public class Main
{
  public static void main(String[] args) {
	//Creating array object
	String subjectArray1[] = new String[5];
	    
	//initializing
        subjectArray1[0]="Java";  
        subjectArray1[1]="Oracle";  
        subjectArray1[2]="SQL";  
        subjectArray1[3]="Spring";  
        subjectArray1[4]="Hibernate";  
        
        //Print array elements
        System.out.println("Elements of subjectArray1:"); 
        for(int i=0;i<subjectArray1.length;i++)
           System.out.println(subjectArray1[i]);  
        
        //Another approach to create an array
        //Creating array object
	String subjectArray2[] = {"Java", "Oracle", "SQL", "Spring", "Hibernate"};
	    
	//Print array elements
	System.out.println("Elements of subjectArray2:"); 
        for(int i=0;i<subjectArray2.length;i++)
           System.out.println(subjectArray2[i]);  	  
   }
}

Output

Elements of subjectArray1:
Java
Oracle
SQL
Spring
Hibernate
Elements of subjectArray2:
Java
Oracle
SQL
Spring
Hibernate

Change an Array Element

public class Main
{
  public static void main(String[] args) {
        //Creating array object
	String subjectArray[] = {"Java", "Oracle", "SQL", "Spring"};
	    
	//Print array elements
	System.out.println("Array Elements:"); 
        for(int i=0;i<subjectArray.length;i++) {
            System.out.println(subjectArray[i]); 
        }
        
        subjectArray[2]  = "Hibernate";
        
        //Print array elements
	System.out.println("Array Elements after change:"); 
        for(int i=0;i<subjectArray.length;i++) {
            System.out.println(subjectArray[i]); 
        }
        
  }
}

Output

Array Elements:
Java
Oracle
SQL
Spring
Array Elements after change:
Java
Oracle
Hibernate
Spring

For-Each Loop on Java Array

Syntax: for-each

for (dataType variable : arrayName) {
  ...
}

Example

public class Main
{
  public static void main(String[] args) {
        //Creating array object
	String subjectArray[] = {"Java", "Oracle", "SQL", "Spring"};
	    
	//Print array elements
	System.out.println("Array Elements:"); 
        for (String subject : subjectArray) {
            System.out.println(subject); 
        }
        
  }
}

Output

Array Elements:                                                                       
Java
Oracle
SQL
Spring

Passing Array as an Argument to a Method

public class Main
{
    static void printArray(String[] subjectArray){
        //Print array elements
	System.out.println("Array Elements:"); 
        for (String subject : subjectArray) {
            System.out.println(subject); 
        }        
    }
    
    public static void main(String[] args) {
        //Creating array object
	String subjectArray[] = {"Java", "Oracle", "SQL", "Spring"};
	//Passing array to method
	printArray(subjectArray);
   }
}

Output

Array Elements:                                                                       
Java
Oracle
SQL
Spring

Return Array from a Method

public class Main
{
    static String[] createArray(){
        //Creating array object
	String subjectArray[] = {"Java", "Oracle", "SQL", "Spring"};
        return subjectArray;
    }
    
    public static void main(String[] args) {
	 //Get array from a method
	 String[] subjectArray = createArray();
	    
        //Print array elements
	System.out.println("Array Elements:"); 
        for (String subject : subjectArray) {
            System.out.println(subject); 
        }
   }
}

Output

Array Elements:                                                                       
Java
Oracle
SQL
Spring

ArrayIndexOutOfBoundsException

JVM will throw ArrayIndexOutOfBoundsException if you want to access any array element from the negative index or from a index which is equal to or greater than array size. An array index can not be negative.

public class Main
{
	public static void main(String[] args) {
        //Creating array object
	    String subjectArray[] = {"Java", "Oracle", "SQL", "Spring"};
	    
	    //Try to Print array element from 4th index
	    System.out.println(subjectArray[4]); 
        
	}
}

Output

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 4                
        at Main.main(Main.java:8)

Class Name of an Array

As we discussed earlier, Java arrays are the objects of dynamically created or proxy class. We can get the name of dynamically created class by reflection.

public class Main
{
    public static void main(String[] args) {
        //Create array
        int numberArray[]={11,12,13};  
        
        //retrieve class of array by reflection
        Class arrayClass = numberArray.getClass();
        
        //Get class neme from class
        String arrayClassName = arrayClass.getName();  
        //Print array class name 
        System.out.println("Array class name: " + arrayClassName); 
    }
}

Output

Array class name: [I

Multidimensional Array

Syntax: Declare an Array

dataType[][] arr;  

dataType [][]arr;

dataType arr[][];  

dataType []arr[];

Syntax: Instantiate an Array

arrayReferenceVariable = new datatype[rowSize][columnSize];

Syntax: Insert elements to an Array

arrayReferenceVariable = {{element11, element12, ..., element1n}, 
{element21, element22, ..., element2n}...{elementm1, elementm2, ..., elementmn};

Syntax: Insert elements to an Array

arrayReferenceVariable[0][0] = element11;
arrayReferenceVariable[0][1] = element12;
arrayReferenceVariable[0][2] = element13;
arrayReferenceVariable[1][0] = element21;
.
.
.
arrayReferenceVariable[m-1][n-1] = elementmn;

Example

public class Main
{
  public static void main(String[] args) {
	//Creating multi-dimensional array
        int numberArray[][]={{11,12,13},{21,22,23},{31,32,33}};  
        //Printing two dimensional array  
        for(int i=0;i<3;i++){  
         for(int j=0;j<3;j++){  
           System.out.print(numberArray[i][j]+" ");  
         }  
         System.out.println();  
        }  
        
  }
}

Output

11 12 13                                                                              
21 22 23                                                                              
31 32 33

Cloning of an Array

We already discussed above that Array implements Cloneable interface and hence we can create clone of Array using clone() method.

Note: When clone method is applied to single dimensional array, it will do deep copy i.e. actual values but in case of multi-dimensional aaray it will create shallow copy i.e. references.

Example

public class Main
{
    public static void main(String[] args) {
        //Create array object
        String subjectArray[] = {"Java", "Oracle", "SQL", "Spring"};
        
        //Print array elements
        System.out.println("Array Elements:"); 
        for (String subject : subjectArray) {
            System.out.println(subject); 
        }
        
        //Clone Array
        String clonedSubjectArray[] = subjectArray.clone();
        
        //Print cloned array elements
        System.out.println("Cloned Array Elements:"); 
        for (String subject : clonedSubjectArray) {
            System.out.println(subject); 
        }
        
    }
}

Output

Array Elements:
Java
Oracle 
SQL 
Spring 
Cloned Array Elements:
Java
Oracle 
SQL 
Spring

Addition of 2 Matrices

public class Main
{
public static void main(String[] args) {
    //Create 2 matrices of 3x2
    int a[][]={{1,3},{1,0},{1,2}};  
    int b[][]={{0,0},{7,5},{2,1}};  
      
    //Result matrix  
    int c[][]=new int[3][2];  
      
    //add and print addition of 2 matrices  
    for(int i=0;i<3;i++){  
        for(int j=0;j<2;j++){  
        c[i][j]=a[i][j]+b[i][j];  
            System.out.print(c[i][j]+" ");  
        }  
            System.out.println();  
        }
    }
}

Output

1 3 
8 5
3 3

Multiplication of 2 Matrices

Primary condition of multiplying 2 matrices is that columns of 1st matrix must be equal to rows of 2nd matrix.

public class Main
{
    public static void main(String[] args) {
        //Create 2 matrices of 3x2
        int a[][]={{1,3},{1,5},{1,2}};  
        int b[][]={{2,3,5},{2,1,6}};  
          
        //Result matrix  
        int c[][]=new int[3][2];  
          
        //Print Multiplication of 2 matrices  
        for(int i=0;i<3;i++){  
            for(int j=0;j<2;j++){  
                c[i][j]=0; 
                for(int k=0;k<2;k++) {
                    c[i][j]+=a[i][k]*b[k][j];  
                }
                System.out.print(c[i][j]+"   ");  
            }  
                System.out.println();  
        }
    }
}

Output

8   6
12   8
6   5

Anonymous Array

8   6
12   8
6   5

Output

8   6
12   8
6   5

Interview Questions on Arrays