checker/tests/nullness/FlowField.java

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

@org.checkerframework.framework.qual.DefaultQualifier(Nullable.class)
public class FlowField {

  public @Nullable String s = null;

  void test() {
    if (s != null) {
      s.startsWith("foo");
    }
  }

  static String field = "asdf";

  static {
    field = "asdf";
  }

  void testFields() {
    // :: error: (dereference.of.nullable)
    System.out.println(field.length());
  }

  // Fowrard reference to static finals
  void test1() {
    nonnull.toString();
  }

  static final String nonnull = new String();

  class A {
    protected String field = null;
  }

  class B extends A {
    void test() {
      assert field != null : "@AssumeAssertion(nullness)";
      field.length();
    }
  }

  static class BooleanWrapper {
    @Nullable Object b;
  }

  @Nullable BooleanWrapper bw;

  void testBitwise(@NonNull FlowField a, @NonNull FlowField b) {
    Object r;
    if (a.bw != null) {
      if (b.bw != null) {
        r = a.bw.b;
        r = b.bw.b;
      }
    }
    if (a.bw != null && b.bw != null) {
      r = a.bw.b;
      r = b.bw.b;
    }
  }

  void testInstanceOf(@NonNull FlowField a) {
    if (!(a.s instanceof String)) {
      return;
    }
    @NonNull String s = a.s;
  }

  void testTwoLevels(@NonNull FlowField a, BooleanWrapper bwArg) {
    // :: error: (dereference.of.nullable)
    if (!(a.bw.hashCode() == 0)) // warning here
    return;
    Object o = a.bw.b; // but not here
  }
}