Java provides various data types just like any other dynamic languages such as boolean, char, int, unsigned int, signed int, float, double, long, etc in total providing 7 types where every datatype acquires different space while storing in memory. When you assign a value of one data type to another, the two types might not be compatible with each other. If the data types are compatible, then Java will perform the conversion automatically known as Automatic Type Conversion, and if not then they need to be cast or converted explicitly. For example, assigning an int value to a long variable.
| Datatype | Bits Acquired In Memory |
|---|---|
| boolean | 1 |
| byte | 8 (1 byte) |
| char | 16 (2 bytes) |
| short | 16(2 bytes) |
| int | 32 (4 bytes) |
| long | 64 (8 bytes) |
| float | 32 (4 bytes) |
| double | 64 (8 bytes) |
Widening or Automatic Type Conversion
Widening conversion takes place when two data types are automatically converted. This happens when:
- The two data types are compatible.
- When we assign a value of a smaller data type to a bigger data type.
For Example, in java, the numeric data types are compatible with each other but no automatic conversion is supported from numeric type to char or boolean. Also, char and boolean are not compatible with each other.
Example:
Java
// Java Program to Illustrate Automatic Type Conversion// Main classclass GFG { // Main driver method public static void main(String[] args) { int i = 100; // Automatic type conversion // Integer to long type long l = i; // Automatic type conversion // long to float type float f = l; // Print and display commands System.out.println("Int value " + i); System.out.println("Long value " + l); System.out.println("Float value " + f); }} |
Int value 100 Long value 100 Float value 100.0
Narrowing or Explicit Conversion
If we want to assign a value of a larger data type to a smaller data type we perform explicit type casting or narrowing.
- This is useful for incompatible data types where automatic conversion cannot be done.
- Here, the target type specifies the desired type to convert the specified value to.
char and number are not compatible with each other. Let’s see when we try to convert one into another.
Java
// Java program to illustrate Incompatible data Type// for Explicit Type Conversion// Main classpublic class GFG { // Main driver method public static void main(String[] argv) { // Declaring character variable char ch = 'c'; // Declaringinteger variable int num = 88; // Trying to insert integer to character ch = num; }} |
Output: An error will be generated
This error is generated as an integer variable takes 4 bytes while character datatype requires 2 bytes. We are trying to plot data from 4 bytes into 2 bytes which is not possible.
How to do Explicit Conversion?
Java
// Java program to Illustrate Explicit Type Conversion// Main classpublic class GFG { // Main driver method public static void main(String[] args) { // Double datatype double d = 100.04; // Explicit type casting by forcefully getting // data from long datatype to integer type long l = (long)d; // Explicit type casting int i = (int)l; // Print statements System.out.println("Double value " + d); // While printing we will see that // fractional part lost System.out.println("Long value " + l); // While printing we will see that // fractional part lost System.out.println("Int value " + i); }} |
Double value 100.04 Long value 100 Int value 100
Note: While assigning value to byte type the fractional part is lost and is reduced to modulo 256(range of byte).
Example:
Java
// Java Program to Illustrate Conversion of// Integer and Double to Byte// Main classclass GFG { // Main driver method public static void main(String args[]) { // Declaring byte variable byte b; // Declaring and initializing integer and double int i = 257; double d = 323.142; // Display message System.out.println("Conversion of int to byte."); // i % 256 b = (byte)i; // Print commands System.out.println("i = " + i + " b = " + b); System.out.println( "\nConversion of double to byte."); // d % 256 b = (byte)d; // Print commands System.out.println("d = " + d + " b= " + b); }} |
Conversion of int to byte. i = 257 b = 1 Conversion of double to byte. d = 323.142 b= 67
Type Promotion in Expressions
While evaluating expressions, the intermediate value may exceed the range of operands and hence the expression value will be promoted. Some conditions for type promotion are:
- Java automatically promotes each byte, short, or char operand to int when evaluating an expression.
- If one operand is long, float or double the whole expression is promoted to long, float, or double respectively.
Example:
Java
// Java program to Illustrate Type promotion in Expressions// Main classclass GFG { // Main driver method public static void main(String args[]) { // Declaring and initializing primitive types byte b = 42; char c = 'a'; short s = 1024; int i = 50000; float f = 5.67f; double d = .1234; // The Expression double result = (f * b) + (i / c) - (d * s); // Printing the result obtained after // all the promotions are done System.out.println("result = " + result); }} |
result = 626.7784146484375
Explicit Type Casting in Expressions
While evaluating expressions, the result is automatically updated to a larger data type of the operand. But if we store that result in any smaller data type it generates a compile-time error, due to which we need to typecast the result.
Example:
Java
// Java program to Illustrate Type Casting// in Integer to Byte// Main classclass GFG { // Main driver method public static void main(String args[]) { // Declaring byte array byte b = 50; // Type casting int to byte b = (byte)(b * 2); // Display value in byte System.out.println(b); }} |
100
Note: In case of single operands the result gets converted to int and then it is typecast accordingly, as in the above example.
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