checker/tests/interning/ExpressionsInterning.java

import org.checkerframework.checker.interning.qual.Interned;

public class ExpressionsInterning {

  class A {
    B b;
  }

  class B {
    C c;

    D d() {
      return new D();
    }

    Boolean bBoolean() {
      return true;
    }
  }

  class C {}

  class D {}

  public Boolean fieldThenMethod(A a) {
    Boolean temp = a.b.bBoolean();
    return temp;
  }

  class Foo {
    public @Interned Foo returnThis(@Interned Foo this, @Interned Foo other) {
      if (other == this) {
        return this;
      } else {
        return null;
      }
    }
  }

  // :: warning: (cast.unsafe.constructor.invocation)
  public @Interned Foo THEONE = new @Interned Foo();

  public boolean isItTheOne(Foo f) {
    return THEONE.equals(f);
  }

  // A warning when interned objects are compared via .equals helps me in determining whether it is
  // a good idea to convert a given class or reference to @Interned -- I can see whether there are
  // places that it is compared with .equals, which I might need to examine.
  public boolean dontUseEqualsMethod(@Interned Foo f1, @Interned Foo f2) {
    // :: warning: (unnecessary.equals)
    return f1.equals(f2);
  }
}