Aptitude

Java OOPS

Arrays

Arrays in Java

Java array is an object which contains elements of a similar data type. Additionally, The elements of an array are stored in a contiguous memory location. It is a data structure where we store similar elements. We can store only a fixed set of elements in a Java array.

Array in Java is index-based, the first element of the array is stored at the 0th index, 2nd element is stored on 1st index and so on.

Unlike C/C++, we can get the length of the array using the length member. In C/C++, we need to use the sizeof operator.

Array

In Java, array is an object of a dynamically generated class. Java array inherits the Object class, and implements the Serializable as well as Cloneable interfaces. We can store primitive values or objects in an array in Java. Like C/C++, we can also create single dimentional or multidimentional arrays in Java.

Moreover, Java provides the feature of anonymous arrays which is not available in C/C++.

Advantages

Code Optimization: It makes the code optimized, we can retrieve or sort the data efficiently.

Random access: We can get any data located at an index position.

Disadvantages

Size Limit: We can store only the fixed size of elements in the array. It doesn't grow its size at runtime. To solve this problem, collection framework is used in Java which grows automatically.

Array Types

There are two types of arrays.

Single Dimetional
Multidimensional Array

Single Dimensional Array in Java

  
dataType[] arr; (or)  
dataType []arr; (or)  
dataType arr[];

Initiaziation of Array in Java

  
arrayRefVar=new datatype[size];

Example :

  
/Java Program to illustrate how to declare, instantiate, initialize  
//and traverse the Java array.  
class Testarray{  
public static void main(String args[]){  
int a[]=new int[5];//declaration and instantiation  
a[0]=10;//initialization  
a[1]=20;  
a[2]=70;  
a[3]=40;  
a[4]=50;  
//traversing array  
for(int i=0;i < a.length; i++)//length is the property of array  
System.out.println(a[i]);  
}}

Declaration, Instantiation and Initialization of Java Array

We can declare, instantiate and initialize the java array together by:

  
int a[]={33,3,4,5};//declaration, instantiation and initialization

Let's see the simple example to print this array.

  
//Java Program to illustrate the use of declaration, instantiation   
//and initialization of Java array in a single line  
class Testarray1{  
public static void main(String args[]){  
int a[]={33,3,4,5};//declaration, instantiation and initialization  
//printing array  
for(int i=0;i < a.length;i++)//length is the property of array  
System.out.println(a[i]);  
}}

output

For-each Loop for Java Array

We can also print the Java array using for-each loop. The Java for-each loop prints the array elements one by one. It holds an array element in a variable, then executes the body of the loop.

The syntax of the for-each loop is given below:

  
for(data_type variable:array){  
//body of the loop  
}

Let us see the example of print the elements of Java array using the for-each loop.

  
//Java Program to print the array elements using for-each loop  
class Testarray1{  
public static void main(String args[]){  
int arr[]={33,3,4,5};  
//printing array using for-each loop  
for(int i:arr)  
System.out.println(i);  
}}

Passing Array to a Method in Java

We can pass the java array to method so that we can reuse the same logic on any array.

Example :

  
//Java Program to demonstrate the way of passing an array  
//to method.  
class Testarray2{  
//creating a method which receives an array as a parameter  
static void min(int arr[]){  
int min=arr[0];  
for(int i=1;iarr[i])  
  min=arr[i];  
  
System.out.println(min);  
}  
  
public static void main(String args[]){  
int a[]={33,3,4,5};//declaring and initializing an array  
min(a);//passing array to method  
}}

Anonymous Array in Java

Java supports the feature of an anonymous array, so you don't need to declare the array while passing an array to the method.

  
//Java Program to demonstrate the way of passing an anonymous array  
//to method.  
public class TestAnonymousArray{  
//creating a method which receives an array as a parameter  
static void printArray(int arr[]){  
for(int i=0;i< arr.length;i++)  
System.out.println(arr[i]);  
}  
  
public static void main(String args[]){  
printArray(new int[]{10,22,44,66});//passing anonymous array to method  
}}

output

Returning Array from the Method

Java supports the feature of an anonymous array, so you don't need to declare the array while passing an array to the method.

  
//Java Program to return an array from the method  
class TestReturnArray{  
//creating method which returns an array  
static int[] get(){  
return new int[]{10,30,50,90,60};  
}  
  
public static void main(String args[]){  
//calling method which returns an array  
int arr[]=get();  
//printing the values of an array  
for(int i=0;i < arr.length;i++)  
System.out.println(arr[i]);  
}}

output

ArrayIndexOutOfBoundsException

The Java Virtual Machine (JVM) throws an ArrayIndexOutOfBoundsException if length of the array in negative, equal to the array size or greater than the array size while traversing the array.

  
/Java Program to demonstrate the case of   
//ArrayIndexOutOfBoundsException in a Java Array.  
public class TestArrayException{  
public static void main(String args[]){  
int arr[]={50,60,70,80};  
for(int i=0;i<=arr.length;i++){  
System.out.println(arr[i]);  
}  
}}

output

  
Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 4
	at TestArrayException.main(TestArrayException.java:5)
50
60
70
80

Multidimensional Array in Java

In such case, data is stored in row and column based index (also known as matrix form).

Sytax

  
dataType[][] arrayRefVar; (or)  
dataType [][]arrayRefVar; (or)  
dataType arrayRefVar[][]; (or)  
dataType []arrayRefVar[];

Example to initiate multidimentional array

  
int[][] arr=new int[3][3];//3 row and 3 column

  
//Java Program to illustrate the use of multidimensional array  
class Testarray3{  
public static void main(String args[]){  
//declaring and initializing 2D array  
int arr[][]={{1,2,3},{2,4,5},{4,4,5}};  
//printing 2D array  
for(int i=0;i<3;i++){  
 for(int j=0;j<3;j++){  
   System.out.print(arr[i][j]+" ");  
 }  
 System.out.println();  
}  
}}

output

Jagged Array in Java

If we are creating odd number of columns in a 2D array, it is known as a jagged array. In other words, it is an array of arrays with different number of columns.

  
//Java Program to illustrate the jagged array  
class TestJaggedArray{  
    public static void main(String[] args){  
        //declaring a 2D array with odd columns  
        int arr[][] = new int[3][];  
        arr[0] = new int[3];  
        arr[1] = new int[4];  
        arr[2] = new int[2];  
        //initializing a jagged array  
        int count = 0;  
        for (int i=0; i< arr.length; i++)  
            for(int j=0; j < arr[i].length; j++)  
                arr[i][j] = count++;  
   
        //printing the data of a jagged array   
        for (int i=0; i < arr.length; i++){  
            for (int j=0; j< arr[i].length; j++){  
                System.out.print(arr[i][j]+" ");  
            }  
            System.out.println();//new line  
        }  
    }  
}

output

What is the class name of Java array?

In Java, an array is an object. For array object, a proxy class is created whose name can be obtained by getClass().getName() method on the object.

  
///Java Program to get the class name of array in Java  
class Testarray4{  
public static void main(String args[]){  
//declaration and initialization of array  
int arr[]={4,4,5};  
//getting the class name of Java array  
Class c=arr.getClass();  
String name=c.getName();  
//printing the class name of Java array   
System.out.println(name);  
  
}}

output

Copying a Java Array

We can copy an array to another by the arraycopy() method of System class.

Syntax of arraycopy method

  
public static void arraycopy(  
Object src, int srcPos,Object dest, int destPos, int length  
)

  
//Java Program to copy a source array into a destination array in Java  
class TestArrayCopyDemo {  
    public static void main(String[] args) {  
        //declaring a source array  
        char[] copyFrom = { 'd', 'e', 'c', 'a', 'f', 'f', 'e',  
                'i', 'n', 'a', 't', 'e', 'd' };  
        //declaring a destination array  
        char[] copyTo = new char[7];  
        //copying array using System.arraycopy() method  
        System.arraycopy(copyFrom, 2, copyTo, 0, 7);  
        //printing the destination array  
        System.out.println(String.valueOf(copyTo));  
    }  
}

output

  
caffein

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Arrays

Arrays in Java