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javaobjectdoublecomparison

Double comparison failing in Java

Why does the first if-statement return true and the second false?

Isn't 100000000000000.032 in the first if-statement also turned into a new Double that is different to dd?

Double dd = 100000000000000.032;
if(dd == 100000000000000.032) {
    System.out.println("gaga");
}

Double ee = 100000000000000.032;
if(dd == ee) {
    System.out.println("gaga");
}
Solution

  • Either you follow Majed Badawi's answer to use equals() because you compare object instances, or you modify your code like below:

    double dd = 100000000000000.032
if( dd == 100000000000000.032 ) 
{
    System.out.println( "gaga" );
}

double ee = 100000000000000.032;
if( dd == ee ) 
{
    System.out.println( "gaga" );
}

    Note that dd and ee are now of the primitive type double (with a lowercase 'D').

    In your sample, the first comparison worked because internally, it was interpreted as:

    … 
if( dd.doubleValue() == 100000000000000.032 ) 
…

    This behaviour is called 'Autoboxing/-unboxing' and was introduced with Java 5; for versions before Java 5, your code would not compile at all.