Java Interview Questions – Part 5
━━━━━━━━━━━━━━━━━━━━━━

01. What is a String in Java?

A String is an object that represents a sequence of characters. Java String objects are immutable, meaning their contents cannot be changed after creation.

Key Points
- Strings are objects in Java
- String objects are immutable
- Commonly used to store and manipulate text

02. What is the Difference Between StringBuilder and StringBuffer?

StringBuilder and StringBuffer are mutable classes used to modify character sequences.

Key Points
- StringBuilder is generally faster in single-threaded code
- StringBuffer synchronizes its methods
- StringBuffer is useful when synchronized access is required

03. What is ArrayList in Java?

ArrayList is a resizable collection that implements the List interface. It stores elements in an ordered sequence and allows duplicate values.

Key Points
- Supports dynamic resizing
- Provides index-based access
- Belongs to the Java Collections Framework

04. What is HashMap in Java?

HashMap stores data as key-value pairs. Each key must be unique, while values can be duplicated.

Key Points
- Uses key-value mapping
- Allows one null key and multiple null values
- Does not guarantee iteration order

05. What is the Difference Between ArrayList and HashMap?

ArrayList stores elements in an indexed sequence, whereas HashMap stores values associated with unique keys.

Key Points
- ArrayList accesses elements using indexes
- HashMap accesses values using keys
- Both belong to the Java Collections Framework

━━━━━━━━━━━━━━━━━━━━━━

UPDATEGADH | Technology Tutorials & Interview Questions

#Java #JavaInterviewQuestions #CoreJava #JavaProgramming #CollectionsFramework #CodingInterview #UPDATEGADH

Java Interview Questions – Part 5
━━━━━━━━━━━━━━━━━━━━━━

21. What is a String in Java?

A String represents a sequence of characters. Java String objects are immutable, meaning their contents cannot be changed after creation.

Code Example

String name = "Java";
System.out.println(name);

Output

Java

22. What is the Difference Between StringBuilder and StringBuffer?

Both classes allow mutable string operations. StringBuilder is generally preferred for single-threaded operations, while StringBuffer synchronizes its methods.

Key Points
- StringBuilder is generally faster without synchronization
- StringBuffer provides synchronized methods
- Both allow string modification

23. What is ArrayList in Java?

ArrayList is a resizable collection that implements the List interface and supports ordered elements and duplicates.

Code Example

import java.util.ArrayList;

ArrayList<String> names = new ArrayList<>();
names.add("Amit");
names.add("Rahul");

System.out.println(names);

Output

[Amit, Rahul]

24. What is HashMap in Java?

HashMap stores values as key-value pairs. Keys are unique, while values can be duplicated.

Code Example

import java.util.HashMap;

HashMap<String, Integer> marks = new HashMap<>();
marks.put("Amit", 85);
marks.put("Rahul", 90);

System.out.println(marks.get("Amit"));

Output

85

25. What is the Difference Between ArrayList and HashMap?

ArrayList stores elements in an indexed sequence, whereas HashMap stores values associated with keys.

Key Points
- ArrayList uses indexes
- HashMap uses keys
- ArrayList permits duplicate elements
- HashMap keys must be unique

━━━━━━━━━━━━━━━━━━━━━━

UPDATEGADH | Technology Tutorials & Interview Questions

#Java #JavaInterviewQuestions #CoreJava #JavaCollections #Programming #UPDATEGADH