Lect5
- 1. Data types, keywords, identifiers in java •What are identifiers in java. •What are keywords how & why they are used? •What are data types in java. 4/10/2019 1Jamsher Bhanbhro(F16CS11)
- 2. Identifiers • Names required for java classes, variables, methods are called identifiers. • Can be A-Z or a-z or in mixture(Alphabets). • Currency character($) can be used as identifier. • _ underscore can be used. • Keywords cannot be used as identifier. • Eg: HelloWorld, Jamsher (may be class names). • A=3; a=5; z=c; x=y, can be the variables. • Sum, Sub, Div can be methods. 4/10/2019 Jamsher Bhanbhro(F16CS11) 2
- 3. Java Keywords • Keywords are reserved names for java. • These can’t be used as identifiers, variables name etc. • Abstract: used for class • Boolean: 0 or 1 true or false • Break: use to break the statement or the condition • Char: for data type • Import, class, switch, case, if else, try, this, throw, void, return, package etc are the java keywords. 4/10/2019 Jamsher Bhanbhro(F16CS11) 3
- 4. Data types in java • When a variable is assigned a memory it is assigned by its data types. • A variable store which type of data is known as data type. • There are basically two data types available in java 1. Primitive data type 2. Non Primitive data type/ Reference data type 4/10/2019 Jamsher Bhanbhro(F16CS11) 4
- 5. Primitive data type • Those data types which are already defined in the java library is known as Primitive data type. • These are built-in or predefined data types. • Java basically supports 8 predefined data types. • Which are byte, short, long, float, double, Boolean, char, int. 4/10/2019 Jamsher Bhanbhro(F16CS11) 5
- 6. 1. Integer Data type • Integer is denoted by int and stores the integer values. • Int data type is a 32-bit signed two's complement integer • Minimum value is - 2,147,483,648 (-2^31) • Maximum value is 2,147,483,647(inclusive) (2^31 -1) • Integer is generally used as the default data type for integral values unless there is a concern about memory. • The default value is 0 • Example: int a = 11, int b = 41 4/10/2019 Jamsher Bhanbhro(F16CS11) 6
- 7. 2. Byte • Byte data type is an 8-bit signed two's complement integer • Minimum value is -128 (-2^7). • Maximum value is 127 (inclusive)(2^7 -1) • Default value is 0. • Byte data type is used to save space in large arrays, mainly in place of integers, since a byte is four times smaller than an integer • For Example: byte a=11, b=41; 4/10/2019 Jamsher Bhanbhro(F16CS11) 7
- 8. 3. Float • Float data-type is a single-precision 32-bit IEEE 754 floating point. • Float is mainly used to save memory in large arrays of floating point numbers. • Default value is 0.0f. • Float data-type is never used for precise values such as currency. • Example: float f1 = 234.5f(f stands for float) 4/10/2019 Jamsher Bhanbhro(F16CS11) 8
- 9. 4. Short • Short datatype is a 16-bit signed two's complement integer • Minimum value is -32,768 (-2^15) • Maximum value is 32,767 (inclusive) (2^15 -1) • Short datatype can also be used to save memory as byte data type. A short is 2 times smaller than an integer • Default value is 0 4/10/2019 Jamsher Bhanbhro(F16CS11) 9
- 10. 5. Long • Long datatype is a 64-bit signed two's complement integer • Minimum value is 9,223,372,036,854,775,808 (- 2^63) • Maximum value is9,223,372,036,854,775,807 (inclusive) (2^63 -1) • This type is used when a wider range than int is needed. • Default value is 0L(L is used for Long) • Example: long a = 100000L, long b = -200000L 4/10/2019 Jamsher Bhanbhro(F16CS11) 10
- 11. 6. Char • char data-type is a single 16-bit Unicode character. • Minimum value is 'u0000' (or 0) . • Maximum value is 'uffff' (or 65,535 inclusive) . • Char data-type is used to store any character • Example: char letterA =‘J‘; 4/10/2019 Jamsher Bhanbhro(F16CS11) 11
- 12. 7. Boolean • Boolean data-type represents one bit of information. • There are only two possible values: true and false. • This data-type is used for simple flags that track true/false conditions. • Default value is false . • Example: boolean one = true, 0=false; 4/10/2019 Jamsher Bhanbhro(F16CS11) 12
- 13. 8. Double • double data-type is a double-precision 64-bit IEEE 754 floating point. • This data-type is generally used as the default data type for decimal values, generally the default choice. • Double data-type should never be used for precise values such as currency. • Default value is 0.0d(d for double) 4/10/2019 Jamsher Bhanbhro(F16CS11) 13
- 14. Reference data-types • These are not predefined data-types. • These are created using defined constructors of the classes. • They are used to access the objects • These are the reference variables • eg: Jamsher ob=new Jamsher(); 4/10/2019 Jamsher Bhanbhro(F16CS11) 14