Indicates a method precondition: the method expects the specified expressions to be non-null when the annotated method is invoked.

For example:

import org.checkerframework.checker.nullness.qual.RequiresNonNull;
import org.checkerframework.checker.nullness.qual.NonNull;
import org.checkerframework.checker.nullness.qual.Nullable;

class MyClass {
  @Nullable Object field1;
  @Nullable Object field2;

  @RequiresNonNull({"field1", "#1.field1"})
  void method1(@NonNull MyClass other) {
    field1.toString();           // OK, this.field1 is known to be non-null
    field2.toString();           // error, might throw NullPointerException
    other.field1.toString();     // OK, other.field1 is known to be non-null
    other.field2.toString();     // error, might throw NullPointerException
  }

  void method2() {
    MyClass other = new MyClass();

    field1 = new Object();
    other.field1 = new Object();
    method1(other);                   // OK, satisfies method precondition

    field1 = null;
    other.field1 = new Object();
    method1(other);                   // error, does not satisfy this.field1 method precondition

    field1 = new Object();
    other.field1 = null;
    method1(other);                   // error, does not satisfy other.field1 method precondition
  }
}

Do not use this annotation for formal parameters (instead, give them a @NonNull type, which is the default and need not be written). The @RequiresNonNull annotation is intended for other expressions, such as field accesses or method calls.