core java in java questions asked in interview – Page 2

What Classes of Exceptions May be Thrown by a Throw Statement

4 July 2026 priya

A throw statement may throw any expression that may be assigned to the Throwable type. In Java, the throw statement is used to explicitly throw an exception. When you use the throw statement, you typically throw an instance of a class that extends either Throwable, which is the base class for all exceptions and errors, or one of its subclasses. The two main subclasses of Throwable are: Exception: This is the class most commonly used for exceptional conditions that a program should…

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To What Value is a Variable of the Boolean Type Automatically Initialized

4 July 2026 priya

The default value of the boolean type is false. In Java, local variables (including boolean variables) are not automatically initialized. If you declare a boolean variable within a method or block without initializing it, the compiler will generate an error if you try to use the variable before giving it a value. For example: java public class Example { public static void main(String[] args) { boolean myBoolean; // Compiler error: variable myBoolean might not have been initialized System.out.println(myBoolean); } } In the above…

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Can Abstract Class Be Instantiated

4 July 2026 priya

No abstract class cannot be instantiated i.e you cannot create a new object of this class No, an abstract class cannot be instantiated in Java. An abstract class is a class that is declared with the abstract keyword. It may have abstract methods (methods without a body) that must be implemented by its subclasses. Abstract classes cannot be instantiated on their own because they may contain incomplete or abstract methods, and it doesn’t make sense to create objects of an…

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What Are The Types of Statements in JDBC

4 July 2026 priya

the JDBC API has 3 Interfaces, (1. Statement, 2. PreparedStatement, 3. CallableStatement ). The key features of these are as follows: Statement This interface is used for executing a static SQL statement and returning the results it produces. The object of Statement class can be created using Connection.createStatement() method. PreparedStatement A SQL statement is pre-compiled and stored in a PreparedStatement object. This object can then be used to efficiently execute this statement multiple times. The object of PreparedStatement class can be…

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How to do Database Connection Using JDBC thin Driver

4 July 2026 priya

This is one of the most commonly asked questions from JDBC fundamentals, and knowing all the steps of JDBC connection is important. import java.sql.*; class JDBCTest { public static void main (String args []) throws Exception { //Load driver class Class.forName (“oracle.jdbc.driver.OracleDriver”); //Create connection Connection conn = DriverManager.getConnection (“jdbc:oracle:thin:@hostname:1526:testdb”, “scott”, “tiger”); // @machineName:port:SID, userid, password Statement stmt = conn.createStatement(); ResultSet rs = stmt.executeQuery(“select ‘Hi’ from dual”); while (rs.next()) System.out.println (rs.getString(1)); // Print col 1 => Hi stmt.close(); } } To establish a database connection using JDBC thin driver in Core Java, you typically follow these steps: Load the JDBC driver: Use Class.forName() to dynamically load the JDBC driver for your database. For a thin driver, this is usually provided…

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How will you Fix the Above Memory Leak

4 July 2026 priya

By providing proper implentation for the key class as shown below with the equals() and hashCode() methods. ….. static class Key { private String key; public Key(String key) { this.key = key; } @Override public boolean equals(Object obj) { if (obj instanceof Key) return key.equals(((Key) obj).key); else return false; } @Override public int hashCode() { return key.hashCode(); } } ….. If you rerun it after making the fix shown above to the MemoryLeak…

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