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Identifiers in Java are composed of Unicode characters, numbers, currency symbols, and connecting characters (like underscores). They are used to give name to objects, classes, and variables in Java. But there are certain naming conventions to write an identifier name.
1) Identifiers must start with a letter, a currency character ($), or a connecting character such as the underscore ( _ ). Identifiers cannot start with a number!
2) After the first character, Identifiers can contain any combination of letters, currency characters, connecting characters, or numbers.
3) In practice, there is no limit to the number of characters an identifier can contain.
5) You can't use a Java keyword as an identifier. We will list them below.
6) Identifiers in Java are case-sensitive; foo and FOO are two different identifiers.
Valid Identifiers: int _abc; int $c; int ______3_a; int _$; int this_is_also_valid_identifier;
Invalid Identifiers: int :b; int -d; int .f; int 7g;
Java Keywords are predefined, reserved words used in Java programming that have special meanings to the compiler. Always remember Keywords cannot be used as an Identifier or Variable name.
The first letter of Class or Interface in Java should be capitalized, and if several words are linked together to form the name, the first letter of the inner words should be uppercase. For classes, the names should typically be nouns.
Example :- Manish, Music, Game , Car, SpeedBraker, DemoClass etc.
The first letter of Class or Interface in Java should be lowercase, and then normal camelCase rules should be used. CamelCase means first letter of word should be lowercase and first letter of other words linked with that word should be in uppercase format.
Example :- displayInfo , getDetails, getAccountInfo etc.
Like methods, the camelCase format should be used, starting with a lowercase letter . Short names which are meaningful sounds good.
Example :- accountBalance, name, etc.
Java constants are created by marking variables static and final. They should be named using uppercase letters with underscore characters as separators:
Example :- MIN_HEIGHT
There are two types of Data types in Java:
■ Primitive Data types : A primitive can be one of eight types: char, boolean, byte, short, int, long, double, or float.
■ Non Primitive Data types : A reference data types are used to refer to (or access) an object. A reference variable is declared to be of a specific type and that type can never be changed. A reference variable can be used to refer to any object of the declared type, or of a subtype of the declared type (a compatible type).
|Type||Bits||Bytes||Minimum Range||Maximum Range|
|byte||8||1||-27||27 - 1|
|short||16||2||-215||215 - 1|
|int||32||4||-231||231 - 1|
|long||64||8||-263||263 - 1|
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