Comparision of double and float primitive types in Java

Consider the following two codes in Java:

// This program prints true
class Geeksforgeeks {
  public static void main(String args[]) {
    float f = 5.25f;
    double d = 5.25
    System.out.println(f == d);
  }
}

Output

true
// But this program prints false.
class Geeksforgeeks {
  public static void main(String args[]) {
    float f = 5.1f;
    double d = 5.1;
    System.out.println(f == d);
  }
}

Output

false

The output is true in first example and false in second. We know that precisions of float and double are different. Size of mantissa for float is 24 and 53 for double.

Let us consider the first example 5.25. Binary representation of integral part is 101 and binary representation of part of dot is 0.01 (needs only two bits)

Let us consider second example 5.1. Binary representation of integral part is same. But binary representation of 0.1 is 1/16 + 1/32 + 1/64 + 1/128 ….. and so on until we reach end of mantissa or sum becomes more than 0.1. In this case we reach end of mantissa and therefore value of 5.1 becomes different in float and double.





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