Java Programming Type Conversion

What is data type conversion?

  • Type conversion is common to assign a value of one type to a variable of another type.
  • There are two types of type conversion.
    • Implicit conversion: Java will perform the conversion automatically if two types are compatible.
    • Explicit conversion: Conversion between two types are incompatible. there is no conversion defined from double to byte. To do so, we must use cast, which performs explicit conversion between incompatible types.

What is implicit conversion?

Implicit conversion: also known as automatic conversions. when one type of data is assigned to another type of variable, implicit conversion will be done if below condition are satisfied.
  • Two types are compatible.
  • Destination variable type is larger than the source type.
Implicit conversion Example:
//Compatible types Example
byte a = 50;
int b;

//automatic conversion happens here if data of byte type is assinged to int variable.
// int variable is always large enought to hold data of byte type.
b = a;

What is explicit conversion?

Explicit conversion: To create a conversion between two incompatible types, we must use a casting. A cast is simply a explict type conversion.
  • Syntax: (target-type) value
  • target type specifies the required type to convert the specified value.
Explicit conversion Example:
int a = 100;
byte b;
// ....
//here data of int type is assigned to variable of byte type. byte type variable is not large enough to hold value of int type data.
//Need casting here, to convert int data to be assigned in byte variable.
b = (byte) a;
Type Casting in java:
// Type conversion in java                                                      
class TypeConversionTest {                                                      
 public static void main(String args[]) {                                       
  byte a;                                                                       
  int b = 310;                                                                  
  double c = 500.14;                                                            
                                                                                
  // Conversion of int to byte.                                                 
  a = (byte) b;                                                                 
  System.out.println("a and b: " + a + " " + b);                                
                                                                                
  // Conversion of double to int.                                               
  b = (int) c;                                                                  
  System.out.println("b and c: " + b + " " + c);                                
                                                                                
  //Conversion of double to byte.                                               
  a = (byte) c;                                                                 
  System.out.println("a and c: " + a + " " + c);                                
 }                                                                              
}  
Output:
a and b: 54 310
b and c: 500 500.14
a and c: -12 500.14

Converting string to integer

int num = Integer.parseInt("302");
Integer.parseInt method is used to convert string into integer value.
If trying to convert empty value or null using Integer.parseInt, throws NumberFormatException exception.
]$ java ArithmeticTest
Exception in thread "main" java.lang.NumberFormatException: For input string: ""
	at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)
	at java.lang.Integer.parseInt(Integer.java:592)
	at java.lang.Integer.parseInt(Integer.java:615)
	at ArithmeticTest.main(ArithmeticTest.java:5)
string str = Integer.toString(302);
Integer.toString method is used to convert integer into string.
If trying to convert null or invalid value using Integer.toString, compiler error will be generated.
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