Hiding fields in java

What is Variable and Method Hiding in Java — Example Tutorial

If Java, if you are not careful you can possibly hide both methods and variables of the superclass. Now you must be wondering what does it mean by hiding a variable or method in Java? A field or variable is said to hide all fields with the same name in superclasses. Similarly, a static method with the same name in a subclass can hide the method of the superclass. This can lead to subtle bugs, especially if you are expecting a different method to be called. In this article, I’ll show you examples of both variables and methods hiding in Java so that you can understand and avoid them in the future.

What are the variable and methods hiding in Java?

Now that you have some ideas of what is variables and methods hiding in Java, it’s time to look at them in more detail. Let’s see code examples to understand method hiding and variable hiding in Java programs.

1. Method Hiding in Java — Example

Method hiding is closely related to method overriding and sometimes programmer hides the method trying to override it. The concept of overriding allows you to write code that behaves differently depending upon an object at runtime.

As I said, a static method with the same name in a subclass can hide the method from a superclass because a static method cannot be overridden in Java.

Here is an example of a method hiding in Java:

class Parent  public static void sleep()  System.out.println("Sleeps at 11 PM"); > > class Child extends Parent  public static void sleep()  System.out.println("Sleeps at 9 PM"); > > public class Code  public static void main(String[] args)  Parent p = new Parent(); Parent c = new Child(); p.sleep(); c.sleep(); > > Output: Sleeps at 11 PM Sleeps at 11 PM

In this example, we assume that p.sleep() will call the sleep() method from Parent class and c.sleep() will call the sleep() method from child class, just like it happens in overriding but because sleep() is a static method, instead of overriding we have hidden the sleep() method.

Since the static method is resolved at compile-time, both are p.sleep() and c.sleep() is resolved to sleep() method of Parent class because the type of p and c variable is Parent. If you remove the static keyword from both methods then it will behave as expected.

Btw, in Java, you cannot override a static method as an instance method or vice-versa. So, if you remove the static keyword from either subclass or superclass method you will get a compile-time error as «This instance method cannot override the static method from Parent» or «This static method cannot hide the instance method from Parent».

In short, a static method with the same name and signature in a subclass can hide a static method of the superclass. You can further join The Complete Java Masterclass to learn more about the static method in Java. It’s one of the most up-to-date courses and covers Java 12.

2. Variable Hiding in Java — Example

A field or variable with the same name in subclass and superclass is known as variable hiding or field hiding in Java. When a variable is hidden, you can use super.variableName to access the value from a superclass.

Here is an example of variable hiding in Java:

public class Parent  int age = 30; > class Child extends Parent  int age = 4; public void age()  System.out.println("Parent's age: " + super.age); System.out.println("Child's age: " + age); > >

As you can see, you can access the superclass value using super.age .

That’s all about method and variable hiding in Java. I don’t encourage you to use the same name in both superclass and subclass unless you are overriding. This behavior can result in confusing code and cause subtle issues. Instead, try to avoid name class and provide a more meaningful name.

1. Can you overload a static method in Java? (answer)
2. My favorite free courses to learn Java? (free courses)
3. Can you override a static method in Java? (answer)
4. 10 Java online courses for beginners (best courses)
5. Why Java doesn’t support operator overloading? (answer)
6. Java or Python? which is a better language for beginners (article)
7. Can you overload or override the main method in Java? (answer)
8. Rules of method overriding in Java? (answer)
9. Difference between overriding, overloading, shadowing, and obscuring in Java? (answer)
10. What is Polymorphism? Method Overloading or Overriding? (answer)
11. 19 Method overloading and overriding interview questions? (list)
12. Constructor and Method Overloading best practices in Java (best practices)
13. Difference between method overloading and overriding? (answer)
14. What is the real use of overloading and overriding? (answer)
15. What is Constructor overloading in Java? (answer)

P. S. — If you are keen to learn Java Programming in-depth but looking for free online courses then you can also check out Java Tutorial for Complete Beginners (FREE) course on Udemy. It’s completely free and you just need an Udemy account to join this course.

Источник

Hiding Fields in Java Inheritance

Or, you can use the annotation of Jackson on getter method of that field and you see there in no such key-value pair in resulted JSON. So, you can just remove getter of field which you want to omit in JSON.

Hiding Fields in Java Inheritance

Within a class, a field that has the same name as a field in the superclass hides the superclass’s field.

public class Test < public static void main(String[] args) < Father father = new Son(); System.out.println(father.i); //why 1? System.out.println(father.getI()); //2 System.out.println(father.j); //why 10? System.out.println(father.getJ()); //why 10? System.out.println(); Son son = new Son(); System.out.println(son.i); //2 System.out.println(son.getI()); //2 System.out.println(son.j); //20 System.out.println(son.getJ()); //why 10? >> class Son extends Father < int i = 2; int j = 20; @Override public int getI() < return i; >> class Father < int i = 1; int j = 10; public int getI() < return i; >public int getJ() < return j; >> 

Can someone explain the results for me?

In java, fields are not polymorphic.

Father father = new Son(); System.out.println(father.i); //why 1? Ans : reference is of type father, so 1 (fields are not polymorphic) System.out.println(father.getI()); //2 : overridden method called System.out.println(father.j); //why 10? Ans : reference is of type father, so 2 System.out.println(father.getJ()); //why 10? there is not overridden getJ() method in Son class, so father.getJ() is called System.out.println(); // same explaination as above for following Son son = new Son(); System.out.println(son.i); //2 System.out.println(son.getI()); //2 System.out.println(son.j); //20 System.out.println(son.getJ()); //why 10? 

The version of the hidden method that gets invoked depends on whether it is invoked from the superclass or the subclass.

i.e. when you invoke a method which is overridden in subclass via a super class reference the super class method is invoked and it access super class members.

This explains following as the reference used is of superclass:

System.out.println(father.i); //why 1? System.out.println(father.j); //why 10? System.out.println(father.getJ()); //why 10? 

Similarly for the following:

System.out.println(son.getJ()); //why 10? 

since getJ() is not defined in Son a Father version is invoked which sees member defined in the Father class.

If you read Hiding Fields; they specifically don’t recommend such method of coding as

Generally speaking, we don’t recommend hiding fields as it makes code difficult to read.

Java Field Hiding, Java Language Specification. If the class declares a field with a certain name, then the declaration of that field is said to hide any and all … Code sampleclass A class B extends A

PDF Form Java Script to Hide / Unhide (Show) Fields

Join our Facebook Q&A Group on PDF Form JavaScript: https://www.facebook.com/groups/pdfformjavascriptIf this video helped you , …

Usage of eclipse warning «field declaration hides another field or variable»?

Eclipse has a java compiler setting called «field declaration hides another field or variable» that can be set to warning/error.

How important is this warning in your opinion?

What is a good standard way to handle this problem?

Code example of where this happens:

I’ve seen solutions where the field is renamed, i.e «fCaption», but that would cause the automatic getters/setters that can be genereated to have odd names ( getfCaption() ). Not unreadable, but ugly.

Edit: Oh yea, there is the possibility to rename the method signature Test(String caption_) or something similar, but that would end up in the javadoc looking weird.

This is a very useful option in my opinion and should be enabled to show a compiler warning. There is an option (in my version at least Eclipse 3.5.2, Java EE feature 1.2.2) to further enable/disable it within constructors and getters/setters to prevent false positives.

I’d say that you just disable this warning — it seems no use in your convention. And no wonder it is ignored by default.

I keep these set to «Error». If a class and its parent both have a field of the same name I don’t want to lose any of my time trying to figure out why I seem to be assigning a value to the field yet it never seems to change!

Java — What is the meaning of local variable hides a field?, 31. It means you’ve got two different variables with the same name — myBoard. One of them is a field in your class. Another one is a local variable, that …

Want to hide some fields of an object that are being mapped to JSON by Jackson

I have a User class that I want to map to JSON using Jackson.

I map this to a JSON string using —

User user = getUserFromDatabase(); ObjectMapper mapper = new ObjectMapper(); String json = mapper.writeValueAsString(user); 

I don’t want to map the securityCode variable. Is there any way of configuring the mapper so that it ignores this field?

I know I can write custom data mappers or use the Streaming API but I would like to know if it possible to do it through configuration?

1. Jackson works on setters-getters of fields. So, you can just remove getter of field which you want to omit in JSON. ( If you don’t need getter at other place.)
2. Or, you can use the @JsonIgnore annotation of Jackson on getter method of that field and you see there in no such key-value pair in resulted JSON.

@JsonIgnore public int getSecurityCode()

Adding this here because somebody else may search this again in future, like me. This Answer is an extension to the Accepted Answer

You have two options: 1. Jackson works on setters-getters of fields. So, you can just remove getter of field which you want to omit in JSON. ( If you don't need getter at other place.) 2. Or, you can use the `@JsonIgnore` [annotation of Jackson][1] on getter method of that field and you see there in no such key-value pair in resulted JSON. @JsonIgnore public int getSecurityCode()

Actually, newer version of Jackson added READ_ONLY and WRITE_ONLY annotation arguments for JsonProperty . So you could also do something like this.

@JsonProperty(access = Access.WRITE_ONLY) private String securityCode; 

@JsonIgnore public int getSecurityCode()

you also can gather all properties on an annotation class

@JsonIgnoreProperties( < "applications" >) public MyClass . String applications; 

If you don’t want to put annotations on your Pojos you can also use Genson.

Here is how you can exclude a field with it without any annotations (you can also use annotations if you want, but you have the choice).

Genson genson = new Genson.Builder().exclude("securityCode", User.class).create(); // and then String json = genson.serialize(user); 

Hiding Fields in Java Inheritance, 5. As per Overriding and Hiding Methods. The version of the hidden method that gets invoked depends on whether it is invoked from the superclass …

How to hide a request field in Swagger API

I want to hide the «id» item in the model, how to do this in java?

to hide a request field in Swagger API v2:

 @ApiModelProperty(hidden = true) private String id; 

@Schema(accessMode = Schema.AccessMode.READ_ONLY) private String id; 

@JsonProperty(access = JsonProperty.Access.READ_ONLY) @ApiModelProperty(accessMode = ApiModelProperty.AccessMode.READ_ONLY) private String id; 

Also see: https://github.com/springfox/springfox/issues/2816

You can use @Hidden with Swagger Core 2.X

@Hidden — Hides a resource, an operation or a property

Example from above link : Marks a given resource, class or bean type as hidden, skipping while reading / resolving.

@Path("/user") @Produces() public class HiddenAnnotatedUserResourceMethodAndData < UserData userData = new UserData(); @POST @Hidden @Operation(summary = "Create user", description = "This can only be done by the logged in user.") @Path("/1") public Response createUser( @Parameter(description = "Created user object", required = true) User user) < userData.addUser(user); return Response.ok().entity("").build(); >@POST @Operation(summary = "Create user", description = "This can only be done by the logged in user.") @Path("/2") public Response createUserWithHiddenBeanProperty( @Parameter(description = "Created user object", required = true) UserResourceBean user) < return Response.ok().entity("").build(); >> 

openapi: 3.0.1 paths: /user/2: post: summary: Create user description: This can only be done by the logged in user. operationId: createUserWithHiddenBeanProperty requestBody: description: Created user object content: '*/*': schema: $ref: '#/components/schemas/UserResourceBean' required: true responses: default: description: default response components: schemas: UserResourceBean: type: object properties: foo: type: string 

The «field hides another field» warning in java, Hiding Fields. Within a class, a field that has the same name as a field in the superclass hides the superclass’s field, even if their types are …

Источник