The Type Promotion Rules

Widening conversions do not lose information about the magnitude of a value.

For example, an int value is assigned to a double variable.

This conversion is legal because doubles are wider than ints.

Java's widening conversions are

• From a byte to a short, an int, a long, a float, or a double
• From a short to an int, a long, a float, or a double
• From a char to an int, a long, a float, or a double
• From an int to a long, a float, or a double
• From a long to a float or a double
• From a float to a double

Widening conversions:

char->int
byte->short->int->long->float->double

  

Here are the Type Promotion Rules:

1. All byte and short values are promoted to int.
2. If one operand is a long, the whole expression is promoted to long.
3. If one operand is a float, the entire expression is promoted to float.
4. If any of the operands is double, the result is double.

In the following code, f * b, b is promoted to a float and the result of the subexpression is float.

public class Main {

  public static void main(String args[]) {
    byte b = 4;
    float f = 5.5f;
    float result = (f * b);
    System.out.println("f * b = " + result);
  }
}

The output:

f * b = 22.0

In the following program, c is promoted to int, and the result is of type int.

public class Main {
  public static void main(String args[]) {
    char c = 'a';
    int i = 50000;
    int result = i / c;
    System.out.println("i / c is " + result);
  }
}

The output:

i / c is 515

In the following code the value of s is promoted to double, and the type of the subexpression is double.

public class Main {
  public static void main(String args[]) {
    short s = 1024;
    double d = .1234;
    double result = d * s;
    System.out.println("d * s is " + result);
  }
}

The output:

d * s is 126.3616

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