checker/tests/nullness/generics/GenericsExampleMin.java

import org.checkerframework.checker.nullness.qual.*;

// This is the example from manual section:
// "Generics (parametric polymorphism or type polymorphism)"
// whose source code is ../../../docs/manual/advanced-features.tex
public class GenericsExampleMin {

  class MyList1<@Nullable T> {
    T t;
    @Nullable T nble;
    @NonNull T nn;

    public MyList1(T t, @Nullable T nble, @NonNull T nn) {
      this.t = t;
      this.nble = nble;
      this.nn = nn;
      this.t = this.nble;
    }

    T get(int i) {
      return t;
    }

    // This method works.
    // Note that it fails to work if it is moved after m2() in the syntax tree.
    // TODO: the above comment seems out-of-date, as method m3 below works.
    void m1() {
      t = this.get(0);
      nble = this.get(0);
    }

    // When the assignment to nn is added, the assignments to t and nble also fail, which is
    // unexpected.
    void m2() {
      // :: error: (assignment)
      nn = null;
      t = this.get(0);
      nble = this.get(0);
    }

    void m3() {
      t = this.get(0);
      nble = this.get(0);
    }
  }

  class MyList2<@NonNull T> {
    T t;
    @Nullable T nble;

    public MyList2(T t, @Nullable T nble) {
      // :: error: (assignment)
      this.t = this.nble; // error
      // :: error: (assignment)
      this.t = nble; // error
    }
  }

  class MyList3<T extends @Nullable Object> {
    T t;
    @Nullable T nble;
    @NonNull T nn;

    public MyList3(T t, @Nullable T nble, @NonNull T nn) {
      // :: error: (assignment)
      this.t = nble;
      this.t = nn;
      // :: error: (assignment)
      this.nn = t;
      // :: error: (assignment)
      this.nn = nble;
      this.nn = nn;
    }
  }

  class MyList4<T extends @NonNull Object> {
    T t;
    @Nullable T nble;
    @NonNull T nn;

    public MyList4(T t, @Nullable T nble, @NonNull T nn) {
      // :: error: (assignment)
      this.t = nble;
      this.t = nn;
      this.nn = t;
      // :: error: (assignment)
      this.nn = nble;
      this.nn = nn;
      this.nn = t;
      this.nble = t;
    }
  }
}