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Ans. Inner join is the intersection of two tables on the condition defined by the where clause i.e will get records from both tables matched by a column.
Outer join is the union of two tables i.e will get all records from both tables and will put null in the columns where related records are not present.
Left Outer join is the left union of two tables i.e all records from the table on the left and values from the right table for related records else null for the columns from right table.
Right Outer join is the right union of two tables i.e all records from the table on the right and values from the left table for related records else null for the columns from left table.
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Ans. <a href="http://javahungry.blogspot.com/2015/03/difference-between-array-and-arraylist-in-java-example.html" rel="nofollow">http://javahungry.blogspot.com/2015/03/difference-between-array-and-arraylist-in-java-example.html</a>
Ans. JDBC is a standard Java Api for Database communication whereas Hibernate is an ORM framework that uses JDBC to connect with Database.
Hibernate is another layer of object table mapping over JDBC that provide a database independent, object oriented and an efficient way of database communication.
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Ans. When a Table Join itself , it's a Self Join. For example - we like to know the pair of department names where first dept has lesser employees than the later.
Select D1.name , D2.name from Dept D1, Dept D2 where D1.employee_count < D2.employee_count
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Ans. A cookie is a small piece of text stored on a user's computer by the browser for a specific domain. Commonly used for authentication, storing site preferences, and server session identification.
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Ans. They are different the way their elements are stored in memory. TreeMap stores the Keys in order whereas HashMap stores the key value pairs randomly.
Which access specifiers can be used with top level class ?
public or default
public or private
public or protected
protected or default
Very frequently asked. Among first few questions in almost all interviews. Among Top 5 frequently asked questions. Frequently asked in Indian service companies (HCL,TCS,Infosys,Capgemini etc based on multiple feedback ) and Epam Systems
Ans. "equals" is the method of object class which is supposed to be overridden to check object equality, whereas "==" operator evaluate to see if the object handlers on the left and right are pointing to the same object in memory.
x.equals(y) means the references x and y are holding objects that are equal. x==y means that the references x and y have same object.
Sample code:
String x = new String("str");
String y = new String("str");
System.out.println(x == y); // prints false
System.out.println(x.equals(y)); // prints true
Ans. Checked exceptions are the exceptions for which compiler throws an errors if they are not checked whereas unchecked exceptions are caught during run time only and hence can't be checked.
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Ans. Its a method which cannot be overridden. Compiler throws an error if we try to override a method which has been declared final in the parent class.
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Ans. There are two types of casting, casting between primitive numeric types and casting between object references. Casting between numeric types is used to convert larger values, such as double values, to smaller values, such as byte values. Casting between object references is used to refer to an object by a compatible class, interface, or array type reference
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Very frequently asked. Usually asked in different variants like Diff between StringBuffer , String Builder ; Difference between StringBuilder and String class; Choice between these classes etc.
Q54. What is the difference between StringBuffer and String class ?
Ans. A string buffer implements a mutable sequence of characters. A string buffer is like a String, but can be modified. At any point in time it contains some particular sequence of characters, but the length and content of the sequence can be changed through certain method calls.
The String class represents character strings. All string literals in Java programs, such as "abc" are constant and implemented as instances of this class; their values cannot be changed after they are created.
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Ans. An interface without any method declaration is called as marker interface. there are 3 in-built interfaces in JVM i.e. serializable, clonable, remote
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