Livedigital Technologies Interview Questions and Answers

ArrayList is a dynamic array that can grow or shrink in size during runtime.

• To create an ArrayList, import java.util.ArrayList and create an instance of it.

• Add elements to the ArrayList using the add() method.

• Access elements using the get() method and remove elements using the remove() method.

• Example: ArrayList<String> names = new ArrayList<String>();

• names.add("John"); names.add("Mary"); names.remove(0);

String is a sequence of characters. String buffer is a mutable sequence of characters.

• String is immutable while String buffer is mutable

• String buffer is more efficient for concatenating multiple strings

• String buffer has methods to insert, append, and delete characters

• Example: String str = "Hello"; StringBuffer sb = new StringBuffer("World");

• Example: str.concat("!"); sb.append("!");

The '==' operator checks for value equality, while '===' checks for both value and type equality.

• The '==' operator performs type coercion, which can lead to unexpected results.

• The '===' operator is more strict and does not perform type coercion.

• For example, 1 == '1' returns true, but 1 === '1' returns false.

• It is generally recommended to use '===' for more predictable and reliable code.

SQL queries for CRUD operations

• CREATE: INSERT INTO table_name (column1, column2, ...) VALUES (value1, value2, ...)

• READ: SELECT column1, column2, ... FROM table_name WHERE condition

• UPDATE: UPDATE table_name SET column1 = value1, column2 = value2, ... WHERE condition

• DELETE: DELETE FROM table_name WHERE condition