Some equal condition didn't work

Question

Why the equal operator dosn't work in this case :

Integer act0 = Integer.valueOf(ac.split("-")[0]);
if (activite_alerte.getActivite().getIdActivite() == act0)) {
    add_notif(profil, ao);
    added = true;
    break;
}

activite_alerte.getActivite().getIdActivite() and act0 are equals 439 but it didn't work but other value work.

another one [http://stackoverflow.com/questions/1700081/why-does-128-128-return-false-but-127-127-return-true-in-this-code](http://stackoverflow.com/questions/1700081/why-does-128-128-return-false-but-127-127-return-true-in-this-code) — Amit.rk3, Aug 05 '15 at 11:46

score 2 · Accepted Answer · answered Aug 05 '15 at 11:44

You're using a boxed integral type Integer. Java permits equality using == for values in the range -128 to +127 since these are "canned" boxed values, so a reference comparison will work for numbers in that range. But your number - 439 - is too big.

You should use .equals() instead for boxed types.

Personally I find this one of the most pernicious aspects of Java.

score 0 · Answer 2 · answered Aug 05 '15 at 12:06

consider the following program:

public class Test {
    public static void main(String args[]) {
        Integer a = new Integer(1);
        Integer b = new Integer(1);
        System.out.println(a == b);
    }
}

The output of this program is false. for float and integer types java has primitive types (int, long, float, double, ...) which are not objects, and the object counterparts (Integer, Long, Float, Double, ...), which are objects. When we write

int a = 3;
int b = 3;

The value 3 is assigned to two variables a and b of primitive types. the two variables can be tested for equality with ==, which in this example will return true.

But if you write this:

Integer a = 3;
Integer b = 3;

Thanks to a feature called autoboxing, this is actually syntactic sugar for:

Integer a = new Integer(3);
Integer b = new Integer(3);

here we have two variables, each one referencing an object of class Integer. The two instances of Integer are distinct, even though semantically they reflect the same underlying int value. In java the == operator applied to variables referencing objects tests whether the two variable are identical, i.e. if they reference the same object instance. Hence

Integer a = 3;
Integer b = 3;
System.out.println(a == b);

will print false, as the two integer created by the autoboxing are distinct. On the other side, this:

Integer a = 3;
Integer b = a;
System.out.println(a == b);

will print true, as b refers the same object created by autoboxing when a is declared.

In addition to testing for identity, for non-primitive variables you can test for equality using the equals() method. So this:

Integer a = 3;
Integer b = 3;
System.out.println(a.equals(b));

will print true. the equals() method is defined in the Object class, hence any class inherits. The one defined in Object checks for identity, but each subclass should override the method to provide the expected semantic. In the case of Integer for example, the redefinition checks the identity of the primitive member variable holding the integer value.

Some equal condition didn't work

2 Answers2