Type Conversion in Java with Examples

Java provides primitive data types with fixed memory sizes, and when assigning values between them, compatible types are converted automatically, while incompatible types require explicit casting.

• Java has 8 primitive data types, each with a fixed memory size.
• Automatic type conversion happens when assigning a smaller type to a larger type (e.g., int -> long).
• Explicit type casting is required when converting a larger type to a smaller type (e.g., double -> int).
• Automatic conversion is safe, while explicit casting may cause data loss.

Types of Type Conversion

Type conversion in Java is done in two ways:

1. 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. 

Int value 100
Long value 100
Float value 100.0

2. 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. 

Output: An error will be generated

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How To Solve The Error:

This error occurs because Java does not allow implicit narrowing conversion from int to char, even if the value can fit. To assign an int to a char, explicit casting is required:

How to do Explicit Conversion? 

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). 

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:  

1. Java automatically promotes each byte, short, or char operand to int when evaluating an expression.
2. If one operand is long, float or double the whole expression is promoted to long, float, or double respectively.

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. 

100

Note: In case of single operands the result gets converted to int and then it is typecast accordingly, as in the above example.

Data Types and Their Memory Allocation

Difference Between Explicit and Implicit Conversion

The below table demonstrates the key difference between Explicit and Implicit Conversion

Note:

• Use implicit conversion when assigning a smaller data type to a larger one (e.g., int → long).

• Use explicit conversion when assigning a larger data type to a smaller one (e.g., double → int) or for incompatible types.