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Common Java Mistakes That Might Lead to OOP Concepts.

Java is a very popular programming language that is used for developing applications and is designed to have a syntax that can be read by humans. Java uses Object Oriented Programming (OOP) concepts which are based on the idea of objects and data types in order to construct a program. There are many reasons why Java is a good option when learning a programming language, but it does have some pitfalls when using certain features. These mistakes might lead to OOP concepts that will help you along the way.

Common Java Mistakes

  • Not using the correct data types

Data types are very important in Java. As with any programming language, you need to know the different data types that are available in order to use them correctly. You can do this by looking at each variable and matching it with the appropriate data type. For example, you might be trying to assign a string of text to an integer variable. If you don’t specify which type it should be, Java will automatically assume that it is a double because they are both numbers. This will cause an error in your program if you were expecting it to be an integer because double cannot hold all the same values as an integer. if you are finding super keyword in java so you are in right place

  • Forgetting semicolons

One common mistake is forgetting semicolons when coding line after line of code on one line. The semicolon marks where one statement finishes and another starts, so forgetting them causes the program not to run properly or at all. This mistake can lead to OOP concepts of where variables need to be declared before they are used in order for the program not to break down when running.

  • Not declaring variables correctly

Another common mistake is not declaring variables correctly before using them in your program which leads to OOP concepts of how objects work with classes and interfaces. Variables must be declared before they are used because Java needs some time for new memory space for them before they are used, otherwise there will be errors when trying to set initial values for them later on in your code.

The class keyword

The class keyword is used to create a new type of object or data type. It can be used to create an instance which refers to the object and it’s name.

Static variables

Java has a static keyword that is used to indicate that a variable, method, or class can be accessed from any part of the code. Static variables are initialized only once and then their values will not change for the entire time the program is running. This can be especially problematic if you are using them to store information that needs to have changes happen every time the program runs.

Instance variables

Instance variables are variables that are specific to an instance. A Instance variables are created when the object is initialized and they don’t exist before the object has been created. They can also be accessed by any methods or constructors in the same class as it is declared in.

Static methods

can be overridden

Java uses static methods which are declared with the keyword static. The keyword static means that the method does not need an object to be called. This is different from a non-static method which requires an object in order to be called. In Java, a static method can be overridden by a subclass which breaks the principle of encapsulation. A technique for handling this problem is using an abstract class that declares variables and methods as abstract and then have subclasses implement them.

Inheritance problems can also occur when overriding a static method. If you change a variable in the parent class but leave it unchanged in a child class, it will result in a polymorphic behavior where one copy of the dynamic type gets changed while the other remains intact. To avoid this, make sure to lock down any variables or members that might need to stay constant throughout all instances of its use.

final methods

Methods in Java can be either declared as final or not. Final methods cannot be overridden and can only be accessed by the class that created them. This is a useful method to use when the functionality of the method doesn’t need to be changed and you want to ensure that it will always behave in a certain way.

Also Read:- Top 5 JavaScript Frameworks You Should Consider in 2022

OOP Concepts

OOP Concepts are very important in Java. An OOP is based on the idea of objects and data types to make programming easier. This is important because it’s based on an object-oriented approach, meaning that you can create your own object, which has its own variables and methods, which you can then interact with, extend, use for inheritance, or anything else.

Object means a real-world entity such as a pen, chair, table, computer, clock, etc. Object-oriented programming is a methodology or paradigm for designing programs using classes and objects. It simplifies software development and maintenance by providing a few concepts:

  • Object
  • Class
  • inheritance
  • Polymorphism
  • Abstraction
  • encapsulation


Any entity which has some state and behavior is known as a commodity. For example, a chair, pen, table, keyboard, bike, etc. It can be physical or logical.

An object can be defined as an instance of a class. An object has an address and takes up some space in memory. Objects can communicate without knowing each other’s data or code details the only thing needed is the type of message accepted and the type of response by the objects.


A collection of objects is called a class. It is a logical unit.

A class can also be defined as a blueprint from which you can create an individual object. The class does not consume space.


When an object acquires all the properties and behaviors of a parent object, it is known as inheritance. It provides code reusability. It is used to achieve runtime polymorphism.


If a task is performed in different ways, it is known as polymorphism. For example: to draw something, for example, shape, triangle, rectangle, etc., to explain in different ways to the customer.

In Java, we use method overloading and method overriding to achieve polymorphism.


Hiding internal details and showing functionality is known as abstraction. For example phone calls, we don’t know internal processing.

In Java, we use abstract class and interface to achieve abstraction.


Binding (or wrapping) code and data together in a single unit is known as encapsulation. For example, a capsule, it is wrapped with various drugs.

A Java class is an example of encapsulation. Java bean is fully encapsulated class because here all data members are private.


Coupling refers to the knowledge or information or dependency of another class. It arises when classes know about each other. If a class has details of information from another class, there is strong coupling. In Java, we use the private, protected and public modifiers to display the visibility level of a class, method, and field. You can use interfaces for weak coupling as there is no concrete implementation.


Cohesion refers to the level of a component that performs a well-defined function. A single well defined task is performed by a highly cohesive method. Weak cohesive method will divide the work into different parts. The package is a highly cohesive package as it contains I/O related classes and interfaces. However, the java.util package is a weak cohesive package as it contains unrelated classes and interfaces.


Association represents the relationship between objects. Here, an object can be associated with a single object or multiple objects. There can be four types of relationships between objects:

  • One to One
  • One to Many
  • Many to One, and
  • Many to Many

Let us understand the relation with real-time examples. For example, a country may have one prime minister, and a prime minister may have one to many ministers. In addition, several MPs may have one prime minister, and several ministers may have many portfolios.

Association can be unidirectional or bidirectional.


Aggregation is one way to achieve association. The Aggregation represents the relationship where one object has other objects as part of its state. It represents a weak relationship between objects. This is also called a has-a relation in Java. As such, inheritance represents an is-a relationship. This is another way of reusing objects. This is another way of reusing objects.


Composition is also a way to achieve association. A Composition represents the relationship where one object has other objects as part of its state. There is a strong relationship between containing object and dependent object. It is the state where objects do not have independent existence. If you delete the parent object, all child objects will be automatically deleted.

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