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javagenericsbridge
St.Antario
St.Antario

Reputation: 27445

Type erasure and bridge method

Consider the following code:

List<Integer>ints= new ArrayList<Integer>();
lst.add(new Object());//no suitable method found for add(Object)...

Why this error is causing? On a compile time we have type erasure, and method boolean add (E e) after erasure will have signature add(Object o). Can you write in detail how ompiler work in this case?

And what about bridge method? As i understood bridge metod have the following implements:

boolean add(Object o){return this.add((Integer) o)}

Upvotes: 1

Views: 344

Answers (3)

Evgeniy Dorofeev
Evgeniy Dorofeev

Reputation: 136102

Bridge methods go in class definition, not in methods, example:

public class Test implements Comparable<Test> {

    public int compareTo(Test o) {
        return ...;
    }
...

compiler will add a bridge method (invisible) here

public int compareTo(Object o) {
    return compareTo((Test)o);
}

because Comparable interface in bytecode has int compareTo(Object o) method and for JVM to detect that the class implements this method the class needs int compareTo(Object o)

Upvotes: 1

Sotirios Delimanolis
Sotirios Delimanolis

Reputation: 280167

You aren't evaluating

lst.add(new Object());

at runtime, you are evaluating it at compile time. At compile time, there is no method List<Integer>#add(Object).

Upvotes: 1

Oliver Charlesworth
Oliver Charlesworth

Reputation: 272687

Type erasure occurs after the compiler has perform type-checking. If it were the other way around, there would be no point in generics!

Upvotes: 7

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