Value ranges of Java Primitive types and type conversion

Value ranges of Java primitive data types:

double: -1.7976931348623157E+308 --- +1.7976931348623157E+308 float: -3.4028235E+38 --- +3.4028235E+38 long: -9223372036854775808 --- 9223372036854775807 int: -2147483648 --- 2147483647 short: -32768 --- 32767 byte: -128 --- 127
double contains all values in float, long, int, short and byte float contains all values in long, int, short and byte long contains all values in int, short and byte int contains all values in short and byte short contains all values in byte

The computer has circuitry that can convert a value of any primitive data type to any other primitive data type

Problem: assigning/converting different data types

Assigning/converting a value in a float to a double:

It will always "fit" because double contains all values in float Therefore: Assigning/converting a value in a float to a double can never result in "overflow" error

Problem: assigning/converting different data types

Assigning/converting a value in a double to a float:

It may result in overflow because some double are not in float !!! Example: 1.0E300 (10³⁰⁰) is a double value But this value cannot be stored as a float

DEMO: demo/02-elem-prog/07-mixed-datatype/StoreFloat.java

Programming rule for the assignment statement b = a in Java

The assignment

b = a

is only allowed if:

The value range of data type of b contains the value range of data type of a

Examples:

short a; int b; float c; double d; d = a; // Allowed c = b; // Allowed a = d; // Disallowed b = c; // Disallowed

DEMO: demo/02-elem-prog/07-mixed-datatype/DemoAssignment.java

Casting: converting one data type to another data type

Casting:
Casting = converting the data representation from one data type to another data type (the conversion happens using computer circuitry)
(The details of a type conversion is complex and not covered in AP Computer Science)

The casting operation in Java is denoted as follows:

(datatype) value // Convert the value into the data type (datatype)

Example:

short a; double d; a = d; // Disallowed a = (short) d; // Allowed, because d was converted to a short data type

DEMO: demo/02-elem-prog/07-mixed-datatype/Casting.java

Rounding float and double to integers

When you assign/convert a float or double to an integer, the decimal part will be truncated

Example:

public class FloatToInt { public static void main(String[] args) { int x; x = (int) 3.14; // x = 3 (0.14 is truncated) x = (int) 6.99; // x = 6 (0.99 is truncated) } }

DEMO: demo/02-elem-prog/07-mixed-datatype/FloatToInt.java

Rounding float and double to integers

If you want to round a float or double values to an integer, first add 0.5 and then cast

Example:

public class RoundFloatToInt { public static void main(String[] args) { int x; x = (int) (3.14+0.5); // = 3.54, cut off --> x = 3 x = (int) (6.99+0.5); // = 7.49, cut off --> x = 7 } }

DEMO: demo/02-elem-prog/07-mixed-datatype/RoundFloatToInt.java

Background information: Computer can only add, subtract, multiple, divide with same type of values

Computer circuitry can only perform operations on 2 values of the same data type

Examples:

double + double double - double double * double double / double float + float float - float float * float float / float long + long long - long long * long long / long int + int int - int int * int int / int short + short short - short short * short short / short byte + byte byte - byte byte * byte byte / byte

Mixed data type operations:

Java will first perform one or more convert (=cast) operation(s) to make operands into the same data type
and then perform the operation

Data type promotion in Java in mixed type operations

When Java performs an arithmetic operation on different data types, the "smaller" data type is converted ("promoted") to the "larger" data type
Data type promotion in arithmetic operations in Java when using different data types:
Additional rule:
In Java, integer operations are always performed (= converted) in int

Example 1 of data type promotion in Java

Example 1:

Evaluate: How Java evaluates a + b float a; (float) a + (float) b // No promotion necessary float b; a + b Result is a float

DEMO: demo/02-elem-prog/07-mixed-datatype/TypePromo1.java

Example 2 of data type promotion in Java

Example 2:

Evaluate: How Java evaluates a + b double a; (int) a + (double) b // Promote a to double int b; (double) a + (double) b a + b Result is a double

DEMO: demo/02-elem-prog/07-mixed-datatype/TypePromo1.java

Example 3 of data type promotion in Java

Example 3:

Evaluate: How Java evaluates a + b byte a; (byte) a + (byte) b // Promote a and b to int byte b; (int) a + (int) b a + b Result is a int

DEMO: demo/02-elem-prog/07-mixed-datatype/TypePromo1.java

Combining assignment with mixed data type operations

Rule: the assignment:

x = value from a mixed data type operation

is only allowed if:

The value range of data type of x contains the value range of result of the mixed data type operation

Examples:

byte a = 1; int b = 2; float c = 3; double d = 4; d = a + c; // Allowed (a + c is a float) a = a + 1; // Disallowed (a + 1 is an int)

DEMO: demo/02-elem-prog/07-mixed-datatype/AssignMixed.java

Mixed type operation: ---- more practice

For each of the assignment statement:

State if the assignment statement has an error (explain why)
If no error, give the value stored in the destination variable

Program:

public class Quiz { public static void main(String[] args) { double answer1 = 3.0 * 5 / 3; double answer2 = 3.0 + 5 / 3; // Tricky ! double answer3 = 5.0 / 3 * 3.0; double answer4 = 5 / 3 * 3.0; // Tricky ! int answer5 = 1 + 2.0 + 3; } }

DEMO: demo/02-elem-prog/07-mixed-datatype/Quiz.java

Mixed type operation: Fahrenheit --> Celsius

Google: Fahrenheit to Celcius (to find conversion formula)

Fix the error(s) in the program below:

public class FtoC { public static void main(String[] args) { double F = 70.0; double C; // Answer should be: 21.11111 C = 5 / 9 * ( F - 32 ); } }

DEMO: demo/02-elem-prog/07-mixed-datatype/FtoC.java