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Integer numerical data types

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• The integer data types (multiple !)
  • The integer data types use the binary number system as encoding method

  • There are a number of different integer types in Java

    The difference between the various integer types is in the size I.e., the number of bytes used in the encoding

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  • Warning:

    Java considers an integer data type of different sizes as different data types !!! (We saw this also when we discussed the float and double)

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  • The integer data types have very similar properties and operations as the floating point data types (float and double

    I will only highlight the differences I will be brief on properties and operations that are similar

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• The various integer types in Java
  • Integer types in Java:

    Type name (keyword)	Number of bytes	Range of values
    byte	1	−128 . . . 127
    short	2	−32768 . . . 32767
    int	4	−2,147,483,648 . . . 2,147,483,647
    long	8	−9,223,372,036,854,775,808 . . . 9,223,372,036,854,775,807

  • And like the case of float and double:

    The computer treats each integer type as a different type The computer can only perform operations on operands of the same date type: byte value + byte value byte value - byte value byte value * byte value And so on... short value + short value short value - short value short value * short value And so on ... The computer cannot perform operations on mixed type operands, such as: byte value + short value byte value - int value byte value * long value And so on... long value + short value byte value - short value int value * short value And so on ... The computer can perform conversion operations that convert from any integer type to any other integer type

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  • Note:

    There is a strict hierarchy among the integer types: The byte type is the least accurate integer type The short type is the more accurate than the byte type The int type is the more accurate than the short type (and the byte type) The long type is the more accurate than the int type (and short and byte) Safe conversions: byte ⇒ short ⇒ int ⇒ long Unsafe conversions: long ⇒ int ⇒ short ⇒ byte

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• Behind the scene of a safe and an unsafe conversions
  • Example of a safe conversion:

    public class Safe { public static void main(String[] args) { int x; short y; y = 1; x = y; // Safe conversion System.out.println(x); } }

    What happens inside the computer (behind the scene):

    The variable y is of the type short and has 16 bits It is assigned the value 1: (The bit pattern 00000000 00000001 encodes the number 1 in using 16 bits The statement x = y; will achieve the following: This statement copies the value from a short typed variable into an more accurate (wider) int typed variable. You cannot lose accuracy !!!

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  • Example of an unsafe conversion:

    public class UnSafe { public static void main(String[] args) { int x; // x uses 4 bytes short y; // y uses 2 bytes x = 65538; // 65538 = 2^16 + 2 y = (short) x; // Unsafe conversion System.out.println(y); //***** Prints 2 !!! // Should be: 65538 !!! } }

    What happens inside the computer (behind the scene):

    The variable x is of the type int and has 32 bits It is assigned the value 65538: (The bit pattern 00000000 00000001 00000000 00000010 encodes the number 65538 in using 32 bits) The statement y = (short) x; will achieve the following: This statement copies the last 16 bits from a int typed variable into an less accurate (narrower) 16 bits short typed variable. You have lost the upper 16 bits bits from the int type variable !!! The conversion will result in incorrect value for large values (values > 65535)

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  • Example Program: (Demo above code)                                                
    • Prog file: click here

    How to run the program:

    Right click on link and save in a scratch directory To compile:   javac UnSafe.java To run:          java UnSafe