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Java

Core Java and object-oriented interview preparation from beginner to advanced.

11 topics107 questions & lessons

Input and Output

1 lessons · Open → 02

Class

12 questions · Open → 03

Object

12 questions · Open → 04

Constructors

12 questions · Open → 05

Access Modifiers

9 questions · Open → 06

Static Keyword

10 questions · Open → 07

Exception Handling

10 questions · Open → 08

Multithreading

14 questions · Open → 09

OOP Principles

11 questions · Open → 10

Arrays and Strings

7 questions · Open → 11

Collections and Stream API

9 questions · Open →

Topics

Optional study guide

See the big picture · Java

From a class to a working object

Start with the diagram, compare the concepts, then apply them to the lesson.

ClassDefines fields and methods.
Constructor callnew creates an instance and invokes a constructor.
Object referenceUse the reference to access accessible members.
Method callThe object performs an operation.

At a glance
Concept	Meaning	Example
Class	A type definition	class Student { ... }
Object	An instance of a class	new Student()
Instance field	State belonging to one object	student.name
Static field	State associated with the class	Student.school

Watch for this: A reference is not the object itself. A null reference cannot be used to call an instance method.

Read the Java learning guide