Understanding Collections.sort() in Java

As the name suggests, the Collections class of java provides a static method called sort() which is used to sort a collection of items in a particular order.

public static <T> void sort(List<T> list, Comparator<? super T> c) {
    list.sort(c);
}

Let’s look at the definition of this method. As we can see, it takes two arguments, one is the List of objects of type T and other is a Comparator which accepts objects of type T and return an order in which list sorting has to be done. In this function definition, we are giving a Comparator to define a sorting order explicitly.

There is one more definition for Collections.sort() method.

public static <T extends Comparable<? super T>> void sort(List<T> list) {
    list.sort((Comparator)null);
}

In this definition, static sort method only accepts the List of objects of type T and it sorts them in a default order. Here we can see that, to sort T in some default order, T must implement the Comparable interface.

It is important to note that,

All wrapper classes_ and String class implement Comparable interface in Java. Wrapper classes are compared by their values, and strings are compared lexicographically. By default, they sort the elements in the ascending order._

To sort the remaining objects of type, T, using Collections.sort() method, either:

1. The object should implement the Comparable interface, or,
2. We should define a custom Comparator that can sort the objects of type T and pass it into our sort function as the second argument.

#java #java-8-feature #programming #sorting #collections-framework

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Collection vs Collections in Java: Difference Between Collection & Collections in Java

Introduction

This article will be looking into one of the most popular questions in Java Language – What is Collection in Java? Also, what do you mean by Collections in Java? Are Collection and Collections the same or different in Java?

What is Collection?

What is Collections?

Conclusion

#full stack development #collection #collection vs collections in java #collections in java #difference between collection and collections in java

How to Install OpenJDK 11 on CentOS 8

What is OpenJDK?

OpenJDk or Open Java Development Kit is a free, open-source framework of the Java Platform, Standard Edition (or Java SE). It contains the virtual machine, the Java Class Library, and the Java compiler. The difference between the Oracle OpenJDK and Oracle JDK is that OpenJDK is a source code reference point for the open-source model. Simultaneously, the Oracle JDK is a continuation or advanced model of the OpenJDK, which is not open source and requires a license to use.

In this article, we will be installing OpenJDK on Centos 8.

#tutorials #alternatives #centos #centos 8 #configuration #dnf #frameworks #java #java development kit #java ee #java environment variables #java framework #java jdk #java jre #java platform #java sdk #java se #jdk #jre #open java development kit #open source #openjdk #openjdk 11 #openjdk 8 #openjdk runtime environment

Why We Need Collection Framework in Java?

A framework is a set of classes and interfaces which provide a ready-made architecture. In order to implement a new feature or a class, there is no need to define a framework. However, an optimal object-oriented design always includes a framework with a collection of classes such that all the classes perform the same kind of task. Before Collection Framework(or before JDK 1.2) was introduced, the standard methods for grouping Java objects (or collections) were Arrays or Vectors, or Hash tables. All of these collections had no common interface. Therefore, though the main aim of all the collections is the same, the implementation of all these collections was defined independently and had no correlation among them. And also, it is very difficult for the users to remember all the different methods, syntax, and constructors present in every collection class.

Collection Framework is a powerful framework in java. This framework defines the most common methods that can be used for any collection of objects. But the question arises that we have an array concept in java then why we need collection framework in java? Now let’s see that why we need collection framework in java with some valid points of difference between array and collection.

#java #java-collections #why we need collection framework in java #java collections framework #framework in java

How to Sort a HashMap by Key in Java

In this tutorial, we’ll take a look at how to sort a HashMap by key in Java.

Let’s go ahead and create a simple HashMap:

Map<String, Integer> unsortedMap = new HashMap();

unsortedMap.put("John", 21);
unsortedMap.put("Maria", 34);
unsortedMap.put("Mark", 31);
unsortedMap.put("Sydney", 24);

unsortedMap.entrySet().forEach(System.out::println);

We’ve got Strings as keys, and Integers as values. Most of the time, you’ll encounter Integers or Strings as keys, and custom objects, Strings or Integers as values. We’ll want to sort this HashMap, based on the String keys.

HashMaps don’t guarantee to maintain the order of its elements in any case. The order can change through time, and they most definitely won’t be printed back in the order of insertion:

John=21
Mark=31
Maria=34
Sydney=24

If you re-run this program, it’ll keep this order, since HashMaps order their elements into bins, based on the hash value of the keys. When printing values from a HashMap, its contents are printed sequentially, so the results will stay the same if we re-run the program multiple times.

#java #how to sort a hashmap by key in java #hashmap #key in java #sort #sort a hashmap by key in java

Introduction to JAVA COLLECTIONS

In this blog we will understand basics of JAVA Collections framework.

What are JAVA Collections and Why do we need them?

The Collection in Java is a framework that provides an architecture to store and manipulate the group of objects.

Collections are like containers that group multiple items in a single unit. For example, a jar of chocolates, a list of names, etc. Collections are used in every programming language and when Java arrived, it also came with few. Let’s see how does it help us:

• Reduces programming effort
• Increases program speed and quality
• Allows interoperability among unrelated APIs
• Reduces effort to learn and to use new APIs
• Reduces effort to design new APIs
• Fosters software reuse

#functional programming #java #collections #functional java #java #introduction to java collections