@Nonnull fields are assumed to be non-null in the constructor

Class fields annotated with @Nonnull are currently assumed to never be null in the class constructor.
@Nonnull only provides guarantees after construction has finished, and checking these fields in the constructor is often useful to avoid boilerplate variables.

A toy example illustrating the issue:

public class AnnotatedClass {
    private @Nonnull String specialValue;
    private @Nonnull Map<String, String> allValues = new HashMap<>();

    /* this constructor incorrectly warns that specialValue might not have been initialized */
    public AnnotatedClass(Iterable<String> values) {
        for (String entry : values)
        {
            String[] split = entry.split("=", 1);
            if (split.length != 2) throw new IllegalArgumentException("Value improperly formatted");

            final String key = split[0];
            final String value = split[1];
            if (value == null) /* needed to avoid warning on the assignment to specialValue later */
                continue;      /* side note: ideally we wouldn't need this, and the IDE           */
                               /*  would recognize that entry.split returns array of non-null     */
            this.allValues.put(key, value);
            if ("specialKey".equals(key))
                this.specialValue = value;
        }
        if (this.specialValue == null) /* the next line incorrectly produces a dead code warning */
            throw new IllegalArgumentException("The provided iterable does not have a special value!");
    }
}

Environment

• Operating System: Windows 10 Enterprise
• JDK version: openjdk 11.0.12 2021-07-20
• Visual Studio Code version: 1.71.2
• Java extension version: v1.11.0

首先，在 VS Code 中使用 Java 扩展和报告的 JDK 环境，通过提供的 AnnotatedClass 示例重现该警告。跟踪构造期间对 @Nonnull 字段的 null 分析行为；当 null 检查和后续赋值不再产生错误警告，同时真正的问题仍会被报告时，即表示完成。