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Identifiers are names in java program. Identifiers can be class name, method name or variable name. Rules for defining identifiers in java: 1) Identifiers must start with letter, Underscore or dollar($) sign.2) Identifiers can’t start with numbers .3) There is no limit on number of characters in identifier but not recommended to have more than […]

We can’t define package statement after import statement in java. Package statement must be the first statement in source file. We can have comments before the package statement

We can’t have more than one package statement in source file. In any java program there can be atmost only 1 package statement. We will get compilation error if we have more than one package statement insource file.

Package is a mechanism to group related classes ,interfaces and enums in to a single module. Package can be declared using the following statement : Syntax : Coding Convention : package name should be declared in small letters. package statement defines the namespace. The main use of package is: 1) To resolve naming conflicts 2) […]

For top level class only two access modifiers are allowed. public and default. If a class is declared aspublic it is visible everywhere.If a class is declared default it is visible only in same package.If we try to give private and protected as access modifier to class we get the below compilation error.Illegal Modifier for […]

Yes we can have multiple classes in single file but it people rarely do that and not recommended. We canhave multiple classes in File but only one class can be made public. If we try to make two classes in Filepublic we get following compilation error.“The public type must be defined in its own file”

When a reference variable doesn’t point to any value it is assigned null.Example : Employee employee;In the above example employee object is not instantiate so it is pointed no where.

Instanceof operator is used to test the object is of which type. Syntax : instanceof Instanceof returns true if reference expression is subtype of destination type. Instanceof returns false if reference expression is null. Example : Since a is integer object it returns true.There will be a compile time check whether reference expression is subtype […]

IS-A RELATIONSHIP HAS- A RELATIONSHIP Is a relationship also known as inheritance Has a relationship also known as composition or aggregation. For IS-A relationship we uses extends keyword For Has a relationship we use new keyword Ex : Car is a vehicle. Ex : Car has an engine. We cannot say Car is an engine […]

‘Has a ‘ relationship is also known as “composition or Aggregation”. As in inheritance we have ‘extends’keyword we don’t have any keyword to implement ‘Has a’ relationship in java. The main advantage of‘Has-A‘ relationship in java code reusability.

‘is a’ relationship is also known as inheritance. We can implement ‘is a’ relationship or inheritance in javausing extends keyword. The advantage or inheritance or is a relationship is reusability of code instead ofduplicating the code.Ex : Motor cycle is a vehicleCar is a vehicle Both car and motorcycle extends vehicle.

Constants in java are created using static and final keywords.1) Constants contains only uppercase letters.2) If constant name is combination of two words it should be separated by underscore.143) Constant names are usually nouns.Ex:MAX_VALUE, MIN_VALUE, MAX_PRIORITY, MIN_PRIORITY

1) Variable names should start with small letters.2) Variable names should be nouns3) Short meaningful names are recommended.4) If there are multiple words every innerword should start with Uppecase character.Ex : string,value,empName,empSalary

1) Method names should start with small letters.2) Method names are usually verbs3) If method contains multiple words, every inner word should start with uppercase letter.Ex : toString()4) Method name must be combination of verb and nounEx : getCarName(),getCarNumber()

1) Interface should start with uppercase letters2) Interfaces names should be adjectivesExample : Runnable, Serializable, Marker, Cloneable

Sun has created Java Coding standards or Java Coding Conventions . It is recommended highly to followjava coding standards.Classnames should start with uppercase letter. Classnames names should be nouns. If Class name is ofmultiple words then the first letter of inner word must be capital letter.Ex : Employee, EmployeeDetails, ArrayList, TreeSet, HashSet

Constants are fixed values whose values cannot be changed during the execution of program. We createconstants in java using final keyword.Ex : final int number =10;final String str=”java-interview –questions”

Character constant is enclosed in single quotes. String constants are enclosed in double quotes. Characterconstants are single digit or character. String Constants are collection of characters.Ex :’2’, ‘A’Ex : “Hello World”

Unicode is a character set developed by Unicode Consortium. To support all languages in the world Javasupports Unicode values. Unicode characters were represented by 16 bits and its character range is 0-65,535.Java uses ASCII code for all input elements except for Strings, identifiers, and comments.