Java Misc

Java array is a data structure where we can store the elements of the same data type. The elements of an array are stored in a contiguous memory location. So, we can store a fixed set of elements in an array.

There are following ways to print an array in Java:

Java for loop
Java for-each loop
Java Arrays.toString() method
Java Arrays.deepToString() method
Java Arrays.asList() method
Java Iterator Interface
Java Stream API

Java for loop

Java for loop is used to execute a set of statements repeatedly until a particular condition is satisfied.

Syntax:

 
for(initialization; condition; increment/ decrement)
{
//statements
}

Example of for loop

In the following example, we have created an array of length four and initialized elements into it. We have used for loop for fetching the values from the array. It is the most popular way to print array in Java.

public class PrintArrayExample1
{  
public static void main(String args[])
{  
//declaration and instantiation of an array
int arr[]=new int[4];	
//initializing elements 
arr[0]=10;
arr[1]=20;  
arr[2]=70;  
arr[3]=40;  
//traversing over array using for loop
for(int i=0;i<arr.length;i++)	//length is the property of the array
System.out.println(arr[i]);  
}
}  

Output:

Java for-each loop

Java for-each loop is also used to traverse over an array or collection. It works on the basis of elements. It returns elements one by one in the defined variable.

Syntax:

Example of for-each loop

In the following example, we have created an array of String type of length four and initialized elements into it. We have used for-each loop to traverse over the array.

public class PrintArrayExample2
{
public static void main(String args[]) 
{
// declaration and instantiation of an array 
String[] city = new String[4];
//initializing elements 
city[0] = "Delhi";
city[1] = "Jaipur";
city[2] = "Gujarat";
city[3] = "Mumbai";
//traversing over array using for-each loop 
for (String str : city) 
{
System.out.println(str);
}
}
}

Output:

Delhi
Jaipur
Gujarat
Mumbai

Java Arrays.toString() method

Java Arrays.toString() is a static method of Arrays class which belongs to java.util package It contains various methods for manipulating array.

Syntax:

It accepts an array of any primitive type as an argument. It returns a string representation of an array that contains a list of array's elements. The elements of an array are converted to String by String.valueOf(int) .

Example of toString() method

import java.util.Arrays;
public class PrintArrayExample3
{
public static void main(String[] args)
{
//declaring and initializing array
int array[] = {34,-10, 56, -9, -33};
//returns string representation of the specified array
System.out.println(Arrays.toString(array));
}
}

Output:

[34, -10, 56, -9, -33]

Java Arrays.deepToString() method

The deepToString() method of Java Arrays class is designed for converting multidimensional arrays to strings.

Syntax:

It accepts an array as a parameter. It returns the String representation of an array.

Example of deepToString() method

In the following example, we have created a two dimensional array of float type.

import java.util.Arrays;
public class PrintArrayExample4 
{
public static void main(String[] args) 
{
//declaration and initialization of two dimensional array of float type
float[][] array = {{1.2f, 2.5f}, {3.9f, 4.0f}, {5.3f, 6.2f}};
System.out.println(Arrays.deepToString(array));
}
} 

Output:

[[1.2, 2.5], [3.9, 4.0], [5.3, 6.2]]

Java Arrays.asList() method

Java Arrays.asList() is a static method of Java Arrays class which belongs to java.util package. It act as a bridge between array based and collection based API.

Syntax:

The method also provides an easy way to create a fixed-size list initialize to contain many elements.

It accepts an array as an argument. It returns the list view of an array.

Example of asList() method

import java.util.Arrays;
public class PrintArrayExample5
{
public static void main(String [] args)
{
//declaration and initialization of two dimensional array
String[] stringArray={"Hello","Java","Programmers"};
System.out.println(Arrays.asList(stringArray));
}

Output:

[Hello, Java, Programmers]

Java Iterator interface

Java Iterator is an interface which belongs to java.util package. The Iterator object can be created by calling iterator() method. It is present in Collection interface. It returns an iterator.

Example of Iterator interface

In the following, example, we have declare an array and initialize elements into it. We first convert the specified array into list by using Arrays.asList() method because iterator allows us to traverse over the collection and then invoke iterator() method of collection class.

import java.util.Arrays;
import java.util.Iterator;
public class PrintArrayExample6
{
public static void main(String[] args) 
{
//declaration and initialization of an array of Double type
Double[] array = { 1.5, 2.6, 3.7, 4.8, 5.9};
//returns an iterator 
Iterator<Double> it = Arrays.asList(array).iterator();
while(itr.hasNext()) //returns a boolean value
{
System.out.println(itr.next());
}
}
}

Output:

1.5
2.6
3.7
4.8
5.9

Java Stream API

A Java Stream is a data structure which is computed on-demand. It doesn't store data. It operates on the source data structure such as collection and array. Java stream API is used to implement internal iteration. It provides several features such as sequential and parallel execution.

Java stream() method

Java stream() is a static method of Java Arrays class which belongs to java.util package. It is used to get a sequential stream of an array.

Syntax:

Where T is the type of array. The method accepts an array whose elements are to be converted into a sequential stream. It returns a sequential IntStream with the specified array as its source.

Java forEach() method

It is a terminal operation. It does not guarantee to respect the encounter order of the stream.

Syntax:

The method accepts an action as a parameter. It is non-interfering action perform on each element. It does not return anything.

There are two terminal operations which we can apply to a stream to print an array.

Get an iterator to the stream

Using stream().forEach()

Example of stream.forEach() method

In the following example, we have used a different way to print an array. The forEach() method is used to iterate over every element of the stream. It is defined in the Iterable and Stream interface.

Inside the forEach() method we have used System.out which is a reference to an object. It represent standard output stream. It has a method called println(). It is an overloaded method which can accept anything as an argument. When we put println() method after member access operator (::), it becomes an expression.

import java.util.Arrays;
public class PrintArrayExample7
{
public static void main(String[] args) 
{
//declaration and initialization of an array of String type
String[] arr = {"Java", "C", "C++", "Python", "Perl"};
//iterating by passing the method reference
Arrays.stream(arr).forEach(System.out::println);
}
}

Output: