Why doesn't Java autobox int to Integer for .equals(Object) method?

Question

I was working on some java classes, and was overriding the .equals(Object) method to test an integer variable of my class, and was surprised when it threw errors saying I could not use the primitive type int, when I was sure it said in the java docs that the compiler will automatically autobox primitive types into the wrapper types for methods.

public boolean equals(Object o)
{
    if (!(o instanceof myClass))
        return false;
    myClass mc = (myClass)o;
    return (this.myInt.equals(mc.getMyInt()));
}

I'm guessing here, but I'm thinking when the method expects an `Integer` it will auto box but when it expects an `Object` (which you may know is intended to be an `Integer`) it will not — Richard Tingle, Aug 24 '14 at 08:26
Autoboxing works on assignments (including parameter assignments). You are trying to use it in `this.myInt.equals(...)` where `myInt` is a primitive. There is no autoboxing available here. — Jim Garrison, Aug 24 '14 at 08:28
assuming `getMyInt()` returns `int`, `this.myInt() == mc.getMyInt()` is fine here — jdphenix, Aug 24 '14 at 08:28
As @Jim said, only assignment are concerned by autoboxing. There're no concept of `implicit` like in Scala that would allow what you expect ;) — Mik378, Aug 24 '14 at 08:32
"I was sure it said in the java docs that the compiler will automatically autobox primitive types into the wrapper types for methods." It doesn't. Have a look at what it really does say. — user207421, Aug 24 '14 at 08:37

score 5 · Accepted Answer · answered Aug 24 '14 at 08:30

I suppose that "this.myInt" is a int and not a Integer. Autoboxing would work in the parameter. Here are some exemple

int a = 1;
int b = 1;
Integer c = 1;
Integer d = 1;

a.equals(b); // doesnt work as equals isn't define on int
c.equals(b); // work, c is an Integer/Object and b is autoboxed
c.equals(d); // work, both are Integer/Object

score 1 · Answer 2 · answered Aug 24 '14 at 08:24

1

You could just use return (this.myInt==mc.getMyInt()); . the equals() method is only defined for Objects.

answered Aug 24 '14 at 08:24

TheLostMind

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This is not clearly defined. In fact, it will only work if the int is small. And even there it might be surprising when comparing int to Integer. – Jonatan Cloutier Nov 08 '19 at 21:11
see: https://stackoverflow.com/questions/25468794/weird-equality-behavior-in-java/25468864#25468864 – Jonatan Cloutier Nov 08 '19 at 21:13

Why doesn't Java autobox int to Integer for .equals(Object) method?

2 Answers2