Category: collections

join two arraylist in java with example

Post author By Rajesh Kumar
Post date June 17, 2020
No Comments on join two arraylist in java with example

In this post, we will learn to join two arraylist in java with example

ArrayList is a dynamic array concept in java. We use ArrayList in so many places.

Syntax

list1.addAll(list2);

From the above syntax list2 will added to list1.

Example

import java.util.ArrayList;
import java.util.List;

public class Join2List {

	public static void main(String[] args) {
		try {
			List<String> list1 = new ArrayList<String>();
			List<String> list2 = new ArrayList<String>();

			list1.add("Rajesh");
			list1.add("Usha");

			list2.add("Kumar");
			list2.add("Nandhini");

			System.out.println("---List1 value before adding list2---");
			for (String string : list1) {
				System.out.println(string);
			}

			// Adding list2 to list1
			list1.addAll(list2);

			System.out.println("---List1 value After adding list2---");

			for (String string : list1) {
				System.out.println(string);
			}
		} catch (Exception e) {
			e.printStackTrace();
		}
	}

}

Output

---List1 value before adding list2---
Rajesh
Usha
---List1 value After adding list2---
Rajesh
Usha
Kumar
Nandhini

Github

https://github.com/rkumar9090/BeginnersBug/blob/master/BegineersBug/src/com/geeks/example/list/Join2List.java

Tags arraylist, java, join

collections java

convert iterator to list in java

Post author By Rajesh Kumar
Post date May 9, 2020
No Comments on convert iterator to list in java

In this tutorial, we will learn convert iterator to list in java

Here we are giving two approach to convert iterator to list in java

Syntax in Java 8

ArrayList<String> list = new ArrayList<String>();
iterator.forEachRemaining(list::add);

Syntax in Java 7

ArrayList<String> list = new ArrayList<String>();
while (iterator.hasNext()) {
  String string = (String) iterator.next();
  list.add(string);
}

Example

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Iterator;

public class IteratorToList {

	public static void main(String[] args) {

		Iterator<String> iterator = Arrays.asList("Rajesh", "Kumar", "Beginners", "Bug").iterator();
		convertToListJava7(iterator);
		convertToListJava8(iterator);

	}

	/**
	 * Java 7 Approach
	 * 
	 * @param iterator
	 * @return
	 */
	public static ArrayList<String> convertToListJava7(Iterator<String> iterator) {
		ArrayList<String> list = new ArrayList<String>();
		while (iterator.hasNext()) {
			String string = (String) iterator.next();
			list.add(string);
		}

		return list;
	}

	/**
	 * Java 8 Apporach
	 * 
	 * @param iterator
	 * @return
	 */
	public static ArrayList<String> convertToListJava8(Iterator<String> iterator) {
		ArrayList<String> list = new ArrayList<String>();
		iterator.forEachRemaining(list::add);
		return list;
	}

}

Github

https://github.com/rkumar9090/BeginnersBug/blob/master/BegineersBug/src/com/geeks/example/list/IteratorToList.java

Iterate list using streams in java

Tags arraylist, collections, iterator, java, java8

collections java

get key and value from hashmap in java

Post author By Rajesh Kumar
Post date February 26, 2020
No Comments on get key and value from hashmap in java

In this tutorial, we will learn about get key and value from hashmap in java

Example Using Java 8


import java.util.HashMap;
import java.util.Map;

public class KeyValueFromHashMap {

	public static void main(String[] args) {
		try {
			Map<String, String> hashMap = new HashMap();
			hashMap.put("1", "Car");
			hashMap.put("2", "Bus");
			hashMap.put("3", "Train");

			// Below code only work above java 8
			hashMap.forEach((key, value) -> {
				System.out.println("Value of " + key + " is " + value);
			});

		} catch (Exception e) {
			e.printStackTrace();
		}
	}
}

Output

Value of 1 is Car
Value of 2 is Bus
Value of 3 is Train

Example using java 7


import java.util.HashMap;
import java.util.Map;

public class KeyValueFromHashMap {

	public static void main(String[] args) {
		try {
			Map<String, String> hashMap = new HashMap();
			hashMap.put("1", "Car");
			hashMap.put("2", "Bus");
			hashMap.put("3", "Train");

			for (Map.Entry<String, String> entry : hashMap.entrySet()) {
				System.out.println(entry.getKey() + " Value is " + entry.getValue());
			}

		} catch (Exception e) {
			e.printStackTrace();
		}
	}
}

Output

1 Value is Car
2 Value is Bus
3 Value is Train

GitHub Url

https://github.com/rkumar9090/BeginnersBug/blob/master/BegineersBug/src/com/geeks/example/KeyValueFromHashMap.java

Check key exists in Hashmap Java

Tags hashmap, java8, key, vaue

collections java

iterate stream with index in Java8

Post author By Rajesh Kumar
Post date February 25, 2020
No Comments on iterate stream with index in Java8

In this post, we will learn to iterate stream with index in Java8

We will come across multiple streams tutorials, but in all the tutorials we never iterate with index numbers

In order to find the current index or other numeric operations index number will help us to get the position

In this tutorial, we are going to use IntStream to get index of the arraylist

Because there is no straight way to get index number in streams

Syntax

IntStream.range(start, end)

Example


import java.util.ArrayList;
import java.util.List;
import java.util.stream.IntStream;

public class IterateStreamWithIndex {

	public static void main(String[] args) {
		try {
			List<String> list = new ArrayList<String>();
			list.add("India");
			list.add("USA");
			list.add("Germany");

			IntStream.range(0, list.size())
					.forEach(x -> System.out.println("The index is " + x + " Value is " + list.get(x)));

		} catch (Exception e) {
			e.printStackTrace();
		}

	}

}

Output

The index is 0 Value is India
The index is 1 Value is USA
The index is 2 Value is Germany

Github

https://github.com/rkumar9090/BeginnersBug/blob/master/BegineersBug/src/com/geeks/example/IterateStreamWithIndex.java

foreach in java8 using streams

sorting operations in java using streams

Tags iterate, java8, streams

collections java

foreach in java8 using streams

Post author By Rajesh Kumar
Post date February 22, 2020
No Comments on foreach in java8 using streams

In this tutorial, we will learn about foreach in java8 using streams

In java8, We can easily iterate a list using streams.

Streams API provided a lot of features. In this post, we are going to see about foreach

Syntax

stream().forEach({operations});

Example


import java.util.ArrayList;
import java.util.List;

public class ForEachExample {

	public static void main(String[] args) {
		try {

			List studentList = new ArrayList();
			Student student = null;

			student = new Student();
			student.setId(1);
			student.setName("Rajesh");
			student.setAddress("Mumbai");
			studentList.add(student);

			student = new Student();
			student.setId(1);
			student.setName("Kumar");
			student.setAddress("Chennai");
			studentList.add(student);

			studentList.stream()
					.forEach(x -> System.out.println("Name is " + x.getName() + " Address is " + x.getAddress()));

		} catch (Exception e) {
			e.printStackTrace();
		}

	}

}

Student.java


public class Student {

	private int id;
	private String name;
	private String address;

	public int getId() {
		return id;
	}

	public void setId(int id) {
		this.id = id;
	}

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public String getAddress() {
		return address;
	}

	public void setAddress(String address) {
		this.address = address;
	}

}

Output

Name is Rajesh Address is Mumbai
Name is Kumar Address is Chennai

sorting operations in java using streams

Iterate list using streams in java

Github

https://github.com/rkumar9090/BeginnersBug/blob/master/BegineersBug/src/com/geeks/example/ForEachExampleUsingStreams.java

Tags arraylist, foreach, java, java8, streams

collections java

sorting operations in java using streams

Post author By Rajesh Kumar
Post date February 12, 2020
No Comments on sorting operations in java using streams

In this example, we learn sorting operations in java using streams

In Java 8 it is easy to sort records from an arraylist

Streams API providing powerful features to sort the records from a list without modifying it

This will returns a stream consisting of the sorted elements

Syntax

Stream sorted()

list.stream().sorted({operations});

Ascending Example

import java.util.ArrayList;
import java.util.List;

public class AscendingSortingStreams {
    public static void main(String[] args) {
        List list = new ArrayList();
        list.add("Ball");
        list.add("Apple");
        list.add("Cat"); // printitng values before sorting
        System.out.println("Values before sorting ");
        list.stream().forEach(x -> System.out.println(x));
        System.out.println("*** Values After sorting ***");
        list.stream().sorted().forEach(x -> System.out.println(x));
    }
}

Output

Values before sorting 
Ball
Apple
Cat
*** Values After  sorting ***
Apple
Ball
Cat

Descending Example

import java.util.ArrayList;
import java.util.Comparator;
import java.util.List;

public class DescendingSortingStreams {
    public static void main(String[] args) {
        List list = new ArrayList();
        list.add("Ball");
        list.add("Apple");
        list.add("Cat");
        // printitng values before sorting
        System.out.println("Values before sorting ");
        list.stream().forEach(x -> System.out.println(x));
        System.out.println("*** Values After sorting ***");
        // Comparator.reverseOrder() will sort the records in descending order
        list.stream().sorted(Comparator.reverseOrder()).forEach(x -> System.out.println(x));
    }
}

Output

Values before sorting 
Ball
Apple
Cat
*** Values After  sorting ***
Cat
Ball
Apple

References

Oracle Docs

filter operations in streams on java

Iterate list using streams in java

Tags collections, java, sorting, streams

collections java

filter operations in streams on java

Post author By Rajesh Kumar
Post date February 11, 2020
No Comments on filter operations in streams on java

In this example we learn filter operations in streams on java

In Java 8 it is easy to filter record from an arraylist

Streams API providing powerful features to filter an record from a list without modifying it

This will returns a stream consisting of the elements of this stream that match the given predicate.

Syntax

Stream filter(Predicate<? super T> predicate)<br><br>

list.stream().filter({operations});

Example

import java.util.ArrayList;
import java.util.List;

public class FilterExample {

	public static void main(String[] args) {

		List studentList = new ArrayList();
		Student student = null;

		student = new Student();
		student.setId(1);
		student.setName("Rajesh");
		student.setAddress("Mumbai");
		studentList.add(student);

		student = new Student();
		student.setId(1);
		student.setName("Kumar");
		student.setAddress("Chennai");
		studentList.add(student);

		studentList.stream().filter(x -> x.getName().equals("Rajesh"))
		.forEach(x -> System.out.print(x.getAddress()));

	}

}

Person.java

public class Student {

	private int id;
	private String name;
	private String address;

	public int getId() {
		return id;
	}

	public void setId(int id) {
		this.id = id;
	}

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public String getAddress() {
		return address;
	}

	public void setAddress(String address) {
		this.address = address;
	}

}

Output

Mumbai

Reference

oracle docs

Iterate list using streams in java

iterate stream with index in Java8

Tags filter, java8, streams

collections java

Iterate list using streams in java

Post author By Rajesh Kumar
Post date February 5, 2020
No Comments on Iterate list using streams in java

In this example, we will learn about iterate list using streams in java with example
It was introduced on Java 8

Features of Streams

No Storage
we can do arithmetic operations
we can filter the data without removing.

Syntax

list.stream().forEach((x) -> {operations});

Example

import java.util.ArrayList;
import java.util.List;

public class IterateListUsingStreams {

    public static void main(String[] args) {
        List list = new ArrayList();
        list.add("Apple");
        list.add("Pineapple");
        list.add("Papaya");
        list.stream().forEach((x) -> System.out.println(x));
    }

}

Output

Apple
Pineapple
Papaya

Example with Pojo

Student.java

public class Student {

	private int id;
	private String name;
	private String address;

	public int getId() {
		return id;
	}

	public void setId(int id) {
		this.id = id;
	}

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public String getAddress() {
		return address;
	}

	public void setAddress(String address) {
		this.address = address;
	}

}

IterateListUsingStreams2 .java

import java.util.ArrayList;
import java.util.List;

public class IterateListUsingStreams2 {

	public static void main(String[] args) {

		List studentList = new ArrayList();
		Student student = null;

		student = new Student();
		student.setId(1);
		student.setName("Rajesh");
		student.setAddress("Chennai");
		studentList.add(student);

		student = new Student();
		student.setId(1);
		student.setName("Kumar");
		student.setAddress("Chennai");
		studentList.add(student);

		studentList.stream().forEach((x) -> System.out.println("Student Id is "+x.getId()+" Name is "+x.getName()));

	}

}

Output

Student Id is 1 Name is Rajesh
Student Id is 1 Name is Kumar

References

https://docs.oracle.com/javase/8/docs/api/java/util/stream/package-summary.html

GitHub

https://github.com/rkumar9090/BeginnersBug/blob/master/BegineersBug/src/com/geeks/example/IterateListUsingStreams.java

https://github.com/rkumar9090/BeginnersBug/blob/master/BegineersBug/src/com/geeks/example/IterateListUsingStreams2.java

iterate stream with index in Java8

ArrayList in java with example

Tags java8, streams

collections java

Check key exists in Hashmap Java

Post author By Rajesh Kumar
Post date January 17, 2020
No Comments on Check key exists in Hashmap Java

Check key exists in Hashmap Java

In below example we are going to Check key exists in Hashmap java

Syntax

<span class="token function">containsKey</span><span class="token punctuation">(</span><span class="token punctuation">)</span>

Example

import java.util.HashMap;
import java.util.Map;

public class KeyExistsHashMapExample {

  public static void main(String[] args) {
    Map<String, String> hashMap = new HashMap<String, String>();
    hashMap.put("1", "Car");
    hashMap.put("2", "Bus");
    hashMap.put("3", "Train");
    boolean isKeyAvaillable = hashMap.containsKey("1");
    if(isKeyAvaillable) {
      System.out.println("The value is "+hashMap.get("1"));
    }
    else {
      System.out.println("Key is not availlable");
    }
  }
}

Output

The value is Car

Reference

https://beginnersbug.com/hashmap-in-java/
https://docs.oracle.com/javase/8/docs/api/java/util/Map.html#containsKey-java.lang.Object-

Download

https://github.com/rkumar9090/BeginnersBug/blob/master/BegineersBug/src/com/geeks/example/KeyExistsHashMapExample.java

Tags hashmap, java, key

collections java

Sort an Arraylist in java with example

Post author By Rajesh Kumar
Post date January 8, 2020
No Comments on Sort an Arraylist in java with example

In this tutorial, we will learn how to Sort an Arraylist in java with example by ascending order using collections class

If you are new to array list refer below link to understand array list
https://beginnersbug.com/arraylist-in-java/

Features

Sort the specified list into ascending order,
This sort is guaranteed to be stable: equal elements will not be reordered as a result of the sort.
The specified list must be modifiable, but need not be resizable.

Syntax

Collections.sort(list);

Example

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

public class SortArrayListExample {
    public static void main(String[] args) {
        List<String> list = new ArrayList();
        list.add("Car");
        list.add("Zebra");
        list.add("Apple");
        list.add("Ball");
        System.out.println("Array list values before sorting \n");
        for (String string : list) {
            System.out.println("Value is " + string);
        }
        // Below sort method will sort your list
        Collections.sort(list);
        System.out.println("\nArray list values after sorting \n");
        for (String string : list) {
            System.out.println("Value is " + string);
        }
    }
}

Output

Array list values before sorting 

Value is Car
Value is Zebra
Value is Apple
Value is Ball

Array list values after sorting 

Value is Apple
Value is Ball
Value is Car
Value is Zebra

Reference

https://docs.oracle.com/javase/7/docs/api/java/util/Collections.html

iterate stream with index in Java8

foreach in java8 using streams

Tags arraylist, collections, java, sorting

Syntax

Example

Output

Github

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Syntax in Java 8

Syntax in Java 7

Example

Github

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Example Using Java 8

Output

Example using java 7

Output

GitHub Url

Related Articles

Syntax

Example

Output

Github

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Syntax

Example

Student.java

Output

Related Article

Github

Syntax

Ascending Example

Output

Descending Example

Output

References

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Syntax

Example

Person.java

Output

Reference

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Features of Streams

Syntax

Example

Output

Example with Pojo

Student.java

IterateListUsingStreams2 .java

Output

References

GitHub

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Syntax

Example

Output

Reference

Download

Features

Syntax

Example

Output

Reference

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