Cognizant Java Developer Interview Questions and Answers

JDK, JVM, and JRE are core components of Java, each serving distinct roles in the development and execution of Java applications.

• JDK (Java Development Kit): A complete toolkit for Java development, including the compiler (javac), libraries, and tools for building Java applications.

• JRE (Java Runtime Environment): Provides the libraries and components necessary to run Java applications, but does not include developm...read more

Functional interfaces are interfaces with a single abstract method, enabling lambda expressions in Java.

• A functional interface can have multiple default or static methods but only one abstract method.

• Common examples include Runnable, Callable, and Comparator.

• They are used primarily in lambda expressions and method references.

• You can define your own functional interfaces using the @FunctionalInterface annotation.

In Java, '==' checks reference equality, while '.equals()' checks value equality for objects.

• == compares memory addresses for reference types.

• Example: String a = new String("test"); String b = new String("test"); a == b returns false.

• .equals() compares the actual content of objects.

• Example: a.equals(b) returns true.

• For primitive types, == compares actual values.

• Example: int x = 5; int y = 5; x == y returns true.

Java is a versatile, object-oriented programming language known for its portability, security, and robust performance.

• Object-Oriented: Java supports encapsulation, inheritance, and polymorphism, allowing for modular and reusable code. Example: Class and object creation.

• Platform Independence: Java code is compiled into bytecode, which can run on any device with a Java Virtual Machine (JVM). Example: Write once, run...read more

A palindrome is a word, phrase, or sequence that reads the same backward as forward, like 'madam' or 'racecar'.

• Definition: A palindrome is a string that remains unchanged when reversed. Example: 'level', 'radar'.

• Ignoring Spaces and Punctuation: When checking for palindromes, spaces and punctuation are often ignored. Example: 'A man, a plan, a canal, Panama!'

• Case Sensitivity: Palindrome checks can be case insensiti...read more

A program to check if a given number is prime or not.

• Create a function to check if a number is prime by iterating from 2 to the square root of the number.

• If the number is divisible by any number other than 1 and itself, it is not prime.

• Handle edge cases like 0, 1, and negative numbers separately.

Inheritance is a fundamental OOP concept allowing a class to inherit properties and methods from another class.

• Promotes code reusability by allowing new classes to use existing class features.

• Supports method overriding, enabling a subclass to provide a specific implementation of a method.

• Facilitates a hierarchical classification of classes, making it easier to manage and understand code.

• Example: If 'Animal' is a s...read more

Static method is a method that belongs to the class itself, not to any specific instance of the class.

• Static methods can be called without creating an instance of the class.

• They are commonly used for utility methods that do not require access to instance variables.

• Static methods are declared using the 'static' keyword.

• Example: Math.max() is a static method in the Math class that returns the maximum of two numbers.