Introduction

If you're a Java programmer, you've probably seen terms like "instance variables" and "static methods." And if you're new to programming in Java, these terms might be confusing. This article will help clarify what they mean—and how they relate to other core concepts in Java.

JAVA

Classes, Objects, and Functional Programming

What is a class?

A class is a blueprint for an object. It defines the fields and methods that are shared by all objects of that type. What is an object?

What is functional programming?

Functional programming allows you to write code in such a way that it returns values but doesn't operate on variables (in other words, it uses functions). This makes your code easier to read and maintain. How do classes relate to objects?

A class can create many different objects from itself if required; for example, when someone makes two dogs of different breeds (like a Labrador Retriever and a German Shepherd) via cloning technology or artificial insemination, they're both based on the same DNA which means they have similar genetics but still look different due to their breed differences! How do objects relate to functions? A function accepts input data (arguments) into memory at runtime and can also return a value to the point in the program that called it using logic statements such as IF/THEN/ELSE statements(Conditional Statements) or FOR loops(Iteration Statements).

Java Static Methods

You can use static methods to create utility classes that do not need to interact with a specific object. Static methods cannot access instance variables, but they can access other static variables and the class's constructor. Static methods are not tied to a particular object, so you can call them without having an instance of the class.

The following code shows how we might write a static method in our program:

public class MathUtils {

public static int sum(int x, int y) {

return x + y;

}

}

Lambda Expressions and Functional Interfaces

A lambda expression is a block of code that you can use as an argument for a method.

A functional interface is an interface that contains only one abstract method. The purpose of these interfaces is to allow you to pass lambda expressions as arguments to methods without having to create an instance of the object first.

You can create a lambda expression by writing the text of your code in curly braces preceded by the word "lambda". When you do this, it will look something like this: { }(parameter). You can also write out individual lines separately and then join them together with semicolons at the end: line1;line2;...lineN; line;; (a semicolon ends every line except for the last one). If there are no parameters being passed into your function, leave off all types and names—just start with "{". For example: "{}". When there are parameters being passed into your function, provide their types separated by commas and enclosed within parentheses after "{}"; however many parameters there are—for example (int i) => i*i. To convert between methods that take functional interfaces and methods that take lambdas:

  • If calling a method using its name like any other object reference casts it before invoking it e.g., someMethod(obj). Use `new' when invoking methods on instances created from classes implementing specific interfaces such as Runnable{}.

Instance Variables and Class Variables

Instance variables are variables that belong to an instance of a class. Class variables are variables that belong to the class itself and can be accessed by all instances of the class. The name "instance" comes from the fact that each object has its own set of instance variables, while there is only one copy of a class variable shared by all objects belonging to that class.

Class Variables

A simple example illustrates how these two types of variables work: let's say we have an Animal class with one Class Variable called numLegs, which represents how many legs each animal has (e.g., 4 legs for dogs or 3 legs for cats). We also define an Instance Variable named furColor using Java's built-in Color enumeration data type, which includes predefined values such as Red or Blue for integers between 0 and 255 (0 = black; 1 = gray; 2 = blue; 3 = green; 4 = cyan/aqua; 5 = magenta/pink). The following code snippet shows how this would work:

The Difference Between Memory Heap and Stack in Java

In this section, you’ll learn about the difference between memory heap and stack in Java. The stack is used for storing method calls, while the heap is used for storing objects (and arrays).

The stack is more efficient than the heap because it doesn’t need to check against null values when creating an object inside a method call. In addition, it doesn’t have to check for null values when accessing an object reference from inside another method call. However, since objects are stored on the heap and not on the stack, they can be accessed from anywhere in your code since they don't disappear after the execution of any single method call or block of code.*

HashMap vs HashTable vs TreeMap in Java

Hashtable is a key-based hashtable data structure that was introduced in JDK 1.0. The keys are used to store the elements and their values. Each element in a Hashtable has a key value, which is unique among all the other elements stored in it. Whenever you create an instance of Hashtable, it automatically creates its internal array of buckets and stores them in memory. You can know how many buckets are created using getHashTableSize() method or by calling getClass().getDeclaredMethod("size", new Class[0]).

HashMap is another value-based hashtable data structure that was introduced in JDK 1.2 as part of the java collections framework

TreeMap is a sorted map which means that it stores the keys in an ordered fashion so you can easily search for them based on their values (for example from highest to lowest). However, unlike Hashtable where insertion order doesn't matter at all (because bucket size is fixed), insertion order does matter with TreeMaps because if your hash function gives different hash values for equal objects then they will not be stored at the same position within the tree which could cause O(log n) worst-case performance for entire operation instead of constant O(1) time complexity like with HashMap

How to Implement an Immutable Class in Java?

What is an immutable class?

An immutable class is a class that cannot be changed after it has been created. That means you cannot modify the object state, its fields, or any of its methods after initialization.

Why should we use immutable classes?

Immutable classes are highly useful in multi-threaded applications because they do not allow concurrent modification of the same state without proper synchronization efforts. This makes it easier to reason about thread safety issues as well

How to implement an Immutable Class in Java?

The easiest way to implement an immutable class is simply by extending from java's built-in java. lang.Object class which has no methods by default and therefore can't be modified (immutability). You can also create your own parent class for this purpose if you want some functionality for your custom immutable types like "toString()" method etc., but this will only work if all subclasses of this parent have no fields or methods themselves.

You must learn about these core concepts if you want to program in Java.

In order to program in Java, you need to understand these core concepts. If you don't know how they work, how can you expect to write a working program? If you don't understand them, then your code will likely be buggy and difficult for other people to work with.

  • Classes: A class is like a blueprint for an object (or more precisely, it's the code that makes up an object). You can think of it as a cookie cutter—you use it once and then throw away the mold after making all your cookies with it. It's reusable!
  • Methods: Think of methods like tools in your toolbox. They let you do stuff! The most common method is main() because every program has one; if there were no main() method then the computer would have no idea what code should run when starting up any application written in Java—which would make things pretty confusing for everyone involved (including our beloved computers).

Conclusion

Java is a powerful programming language that you will use to write many applications. It can be used to create desktop, web, and mobile apps. The knowledge of these core concepts is vital if you want to learn Java quickly and efficiently.

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