Skip Top Navigation Bar

Introduction to Type Conversions with Casting

In Introduction to Arithmetic Expressions tutorial, we learned that there are two different types of division.

This means that division functions in two different ways:

  • If both operands are of type int, the result truncates (removes) any remainder. This is considered integer division. For example:
    • 7 / 2 results in 3, the decimal portion is not included.
    • 4 / 2 results in 2, there is no remainder in this case.
  • If one or both operands are of type double, the result includes the remainder. For example:
    • 7.0 / 2 results in 3.5. Similarly, 7 / 2.0 and 7.0 / 2.0 will also result in 3.5.
    • 4.0 / 2 results in 2.0. Similarly, 4 / 2.0 and 4.0 / 2.0 will also result in 2.0.

There are often times when you have two int values or variables and want to compute division and have the result include the remainder. There are also times when one of the values is a double and we need the whole part of the division.

You can convert the type of a value through casting. Casting Conversions converts the type of an expression to the type specified. It is done by placing the desired type in parenthesis prior to the expression. In the case of wanting one or both of the operands to be a double, we can cast to a double as follows:

int value1 = 5; 
int value2 = 2; 
double result = (double)value1 / value2;

This will temporarily convert the type of value1 to a double. When the division is performed, result will now be assigned 2.5, instead of 2. You could also typecast value2 or both value1 and value2 to achieve this same result.

Your Turn

Let's try this in the Java Playground.

  • Run the code to determine what is stored in result.
  • Modify the code to typecast value2 to a double instead of value1.
  • Run the code. What do you notice about this result?
  • Modify the code to typecast both value1 and value2 to a double.
  • Run the code. What do you notice about this result?

Your Turn: Computing An Average

Consider you want to compute your average for a class. You have two int values:

  • the sum of all the grades and
  • the number of grades that you have.

When we compute the average of the the two int values, it will truncate the result, essentially always rounding down.

Instead, you might want to have the real-number average.

Let's try this in the Java Playground.

  • Cast sumGrades to be a double by putting (double) in front of sumGrades when computing average.
  • Run the code. What do you notice about this result?
  • Move the cast from sumGrades to gradeCount.
  • Run the code. What do you notice about this result?
  • Cast both sumGrades and gradeCount.
  • Run the code. What do you notice about this result?

Data Conversions

When we typecast from an int to a double, this is considered a widening conversion since the int value fits into the double type without any loss of data.

When we typecast from a double to an int, this is considered a narrowing conversion since the double value might need to be truncated to fit into the int type thereby losing some data.

Your Turn

Let's try this in the Java Playground.

  • Cast average to an int.
  • Run the code.
  • How does this change the value stored in truncatedAverage?

Next Learn Tutorial

Learn: Introduction to Console Input and Output