将对象添加到数组[重复项]

Question

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NullPointerException when Creating an Array of objects [duplicate]（9个答案）

关闭2分钟前。

我想创建一个使用Javassist将注释添加到已编译Java类中的代码。我试过了：

        ClassFile classFile = ClassPool.getDefault().get("org.poc.Hello").getClassFile();
        ConstPool constPool = classFile.getConstPool();
        AnnotationsAttribute attr= new AnnotationsAttribute(constPool, AnnotationsAttribute.visibleTag);
        Annotation annotation = new Annotation("Author", constPool);
        Annotation author = new Annotation("Description", constPool);
        Annotation[] array = new Annotation[4];
        array[0] = annotation;
        array[1] = author;

        attr.setAnnotations(array);
        classFile.addAttribute(attr);
        classFile.write(new DataOutputStream(new FileOutputStream("src/test/org/poc/Foo.class")));

但是当我运行它时，我在这一行得到了NPE：attr.setAnnotations(array);您知道将对象添加到数组中的正确方法是什么吗？

Answer 1

由于new Annotation[4];，您将获得空指针异常。您只有2个注释。因此剩余的2将为空。

        ClassFile classFile = ClassPool.getDefault().get("org.poc.Hello").getClassFile();
        ConstPool constPool = classFile.getConstPool();
        AnnotationsAttribute attr= new AnnotationsAttribute(constPool, AnnotationsAttribute.visibleTag);
        Annotation annotation = new Annotation("Author", constPool);
        Annotation author = new Annotation("Description", constPool);
        Annotation[] array = new Annotation[2];
        array[0] = annotation;
        array[1] = author;

        attr.setAnnotations(array);
        classFile.addAttribute(attr);
        classFile.write(new DataOutputStream(new FileOutputStream("src/test/org/poc/Foo.class")));