Insert type casts if necessary to preserve type safety

Question

As the official tutorial about generics type erasure, and this statement is so confusing me. When the type cast inserting might occur exactly? I tried with some simple usages of generics and using javap -c a.class to check the bytecode but it seems no typecasting inserted as I expected.

The so-called duplicated is more about the bridge method using a type cast to ensure there is proper polymorphism while I am wondering what the second statement means exactly.

Insert type casts if necessary to preserve type safety.

Any example could be provided to demonstrate it?

Possible duplicate of [Java Type Erasure: Rules of cast insertion?](https://stackoverflow.com/questions/29587502/java-type-erasure-rules-of-cast-insertion) — Tom, Mar 10 '19 at 05:00

Hearen · Accepted Answer · 2019-03-10T08:21:33.470

In the end, I think Jon Skeet's answer cleared out the confusion.

when generics are used, they're converted into compile-time checks and execution-time casts.

When we try to compile a.java and decompile the a.class, we will see the magic (compiler helps auto-insert type cast).

    List<String> list = new ArrayList<>();
    list.add("hell");
    out.println(list.get(0));

After being decompiled:

    ArrayList var3 = new ArrayList();
    var3.add("hell");
    System.out.println((String)var3.get(0));

Using Legacy Code in Generic Code from the official generic tutorial:

... whenever the resulting code isn't type-correct, a cast to the appropriate type is inserted...

Insert type casts if necessary to preserve type safety

1 Answers1