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DataTypes in Java

DataTypes:
Data types represent the different values to be stored in the variable. In java, there are two types of data types:
  • Primitive data types
  • Non-primitive data types
DataType
Default Value
Default size
boolean
false
1 bit
char
'\u0000'
2 Byte
Byte
0
1 Byte
Short
0
2 Byte
int
0
4 Bytes
long
0L
8Bytes
float
0.0f
4 Bytes
Double
0.0d
8 Bytes

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.
·        Example: byte a = 100, byte b = -50
short
·        Short data type 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 data type can also be used to save memory as byte data type. A short is 2 times smaller than an integer
·        Default value is 0.
·        Example: short s = 10000, short r = -20000
int
·        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 = 100000, int b = -200000

long
  • Long data type is a 64-bit signed two's complement integer
  • Minimum value is -9,223,372,036,854,775,808(-2^63)
  • Maximum value is 9,223,372,036,854,775,807 (inclusive)(2^63 -1)
  • This type is used when a wider range than int is needed
  • Default value is 0L
  • Example: long a = 100000L, long b = -200000L
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
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
·        Example: double d1 = 123.4
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


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 = 'A'

Local Variables

·        Local variables are declared in methods, constructors, or blocks.
·        Local variables are created when the method, constructor or block is entered and the variable will be destroyed once it exits the method, constructor, or block.
·        Access modifiers cannot be used for local variables.
·        Local variables are visible only within the declared method, constructor, or block.
·        Local variables are implemented at stack level internally.
·        There is no default value for local variables, so local variables should be declared and an initial value should be assigned before the first use.

Instance Variables

·        Instance variables are declared in a class, but outside a method, constructor or any block.
·        When a space is allocated for an object in the heap, a slot for each instance variable value is created.
·        Instance variables are created when an object is created with the use of the keyword 'new' and destroyed when the object is destroyed.
·        Instance variables hold values that must be referenced by more than one method, constructor or block, or essential parts of an object's state that must be present throughout the class.
·        Instance variables can be declared in class level before or after use.
·        Access modifiers can be given for instance variables.

Access Control Modifiers

Java provides a number of access modifiers to set access levels for classes, variables, methods and constructors. The four access levels are −
  • Visible to the package, the default. No modifiers are needed.
  • Visible to the class only (private).
  • Visible to the world (public).
  • Visible to the package and all subclasses (protected).

Non-Access Modifiers

Java provides a number of non-access modifiers to achieve many other functionality.
·        The static modifier for creating class methods and variables.
·        The final modifier for finalizing the implementations of classes, methods, and variables.
·        The abstract modifier for creating abstract classes and methods.
·        The synchronized and volatile modifiers, which are used for threads.

Java String

In java, string is basically an object that represents sequence of char values. An array of characters works same as java string. For example:

1.    char[] ch={'j','a','v','a','t','p','o','i','n','t'};  
2.    String s=new String(ch);  
is same as:
1.    String s="javatpoint";  
Java String class provides a lot of methods to perform operations on string such as compare(), concat(), equals(), split(), length(), replace(), compareTo(), intern(), substring() etc.


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