Skip to content

JAVA Type Casting - (Data type convert)

2026-03-04 09:46

Tags: #java

Author: Duke Hsu

Key Concept

Type casting means converting one data type into another. For example, turning an intinto a double .

In Java, there are two main types of casting:

  • Widening Casting(automatic) - Converting a smaller type to a larger type size byte -> short -> char -> int -> long -> float -> double

  • Narrowing Casting(manual) - Converting a larger type to a smaller type size double -> float -> long -> int -> char -> short -> byte

Code Example

Widening Casting - Smaller to Larger- Automatic 

1
2
3
4
5
6
7
8
9
int myInt = 9;

double myDouble = myInt; // smaller type to a larger type: int to double

System.out.println(myInt); //outputs 9


//small to lartge, automatic 
System.out.println(myDouble); //outputs 9.0

Narrowing Casting - Larger to Smaller - Manual 

1
2
3
4
5
6
double myDouble = 9.78d;
int myInt = (int) myDouble; // manual casting: double to int , larger to smaller 

System.out.println(myDouble); //ouputs 9.78

System.out.println(myInt); // outputs 9

float and doubledata type

  • The double data type has higher precision than the float data type .

Note

In Java, the double data type provides higher precision than float.

1
2
3
4
5
double myDouble = 3.14159265358d;
float myFloat = 3.14159265358f;

System.out.prinln(myDouble); //outputs 3.14159265358
System.out.println(myFloat); //outputs 3.1415927

Real-Life Example

Gross profit margin 

1
2
3
4
5
6
7
8
int salesIncome = 5500;
int salesCosts = 3500;


// large data type to small
double grossProfit = (double)salesIncome / salesCosts * 100.0d

System.out.println("The Gross profit margin is : "+ grossProfit); //The Gross profit margin is : 157.14285714285714

References

Java Type Casting - https://www.w3schools.com/java/java_type_casting.asp