What is the difference between field, variable, attribute, and property in Java POJOs?

Question

From here: http://docs.oracle.com/javase/tutorial/information/glossary.html

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• field

  • A data member of a class. Unless specified otherwise, a field is not static.

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• property

  • Characteristics of an object that users can set, such as the color of a window.

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• attribute

  • Not listed in the above glossary

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• variable

  • An item of data named by an identifier. Each variable has a type, such as int or Object, and a scope. See also class variable, instance variable, local variable.

Yes, there is.

Variable can be local, field, or constant (although this is technically wrong). It's vague like attribute. Also, you should know that some people like to call final non-static (local or instance) variables

"Values". This probably comes from emerging JVM FP languages like Scala.

Field is generally a private variable on an instance class. It does not mean there is a getter and a setter.

Attribute is a vague term. It can easily be confused with XML or Java Naming API. Try to avoid using that term.

Property is the getter and setter combination.

Some examples below

public class Variables {

    //Constant
    public final static String MY_VARIABLE = "that was a lot for a constant";

    //Value
    final String dontChangeMeBro = "my god that is still long for a val";

    //Field
    protected String flipMe = "wee!!!";

    //Property
    private String ifYouThoughtTheConstantWasVerboseHaHa;

    //Still the property
    public String getIfYouThoughtTheConstantWasVerboseHaHa() {
        return ifYouThoughtTheConstantWasVerboseHaHa;
    }

    //And now the setter
    public void setIfYouThoughtTheConstantWasVerboseHaHa(String ifYouThoughtTheConstantWasVerboseHaHa) {
        this.ifYouThoughtTheConstantWasVerboseHaHa = ifYouThoughtTheConstantWasVerboseHaHa;
    }

}

There are many more combinations, but my fingers are getting tired :)

If your question was prompted by using JAXB and wanting to choose the correct XMLAccessType, I had the same question. The JAXB Javadoc says that a "field" is a non-static, non-transient instance variable. A "property" has a getter/setter pair (so it should be a private variable). A "public member" is public, and therefore is probably a constant. Also in JAXB, an "attribute" refers to part of an XML element, as in <myElement myAttribute="first">hello world</myElement>.

It seems that a Java "property," in general, can be defined as a field with at least a getter or some other public method that allows you to get its value. Some people also say that a property needs to have a setter. For definitions like this, context is everything.

Dietel and Dietel have a nice way of explaining fields vs variables.

“Together a class’s static variables and instance variables are known as its fields.” (Section 6.3)

“Variables should be declared as fields only if they’re required for use in more than one method of the class or if the program should save their values between calls to the class’s methods.” (Section 6.4)

So a class's fields are its static or instance variables - i.e. declared with class scope.

Reference - Dietel P., Dietel, H. - Java™ How To Program (Early Objects), Tenth Edition (2014)

If you take clue from Hibernate:

Hibernate reads/writes Object's state with its field. Hibernate also maps the Java Bean style properties to DB Schema. Hibernate Access the fields for loading/saving the object. If the mapping is done by property, hibernate uses the getter and setter.

It is the Encapsulation that differentiates means where you have getter/setters for a field and it is called property, withthat and we hide the underlying data structure of that property within setMethod, we can prevent unwanted change inside setters. All what encapsulation stands for...

Fields must be declared and initialized before they are used. Mostly for class internal use.

Properties can be changed by setter and they are exposed by getters. Here field price has getter/setters so it is property.

class Car{
 private double price;
 public double getPrice() {…};
 private void setPrice(double newPrice) {…};
}

<class name="Car" …>
<property name="price" column="PRICE"/>
</class>

Similarly using fields, [In hibernate it is the recommended way to MAP using fields, where private int id; is annotated @Id, but with Property you have more control]

class Car{
  private double price;
}
<class name="Car">
<property name=" price" column="PRICE" access="field"/>
</class>

Java doc says: Field is a data member of a class. A field is non static, non-transient instance variable. Field is generally a private variable on an instance class.

The difference between a variable, field, attribute, and property in Java:

A variable is the name given to a memory location. It is the basic unit of storage in a program.

A field is a data member of a class. Unless specified otherwise, a field can be public, static, not static and final.

An attribute is another term for a field. It’s typically a public field that can be accessed directly.

• In NetBeans or Eclipse, when we type object of a class and after that dot(.) they give some suggestion which are called Attributes.

A property is a term used for fields, but it typically has getter and setter combination.

Variables are comprised of fields and non-fields.

Fields can be either:

1. Static fields or
2. non-static fields also called instantiations e.g. x = F()

Non-fields can be either:

1. local variables, the analog of fields but inside a methods rather than outside all of them, or
2. parameters e.g. y in x = f(y)

In conclusion, the key distinction between variables is whether they are fields or non-fields, meaning whether they are inside a methods or outside all methods.

Basic Example (excuse me for my syntax, I am just a beginner)

Class {    
    //fields    

    method1 {              
         //non-fields    

    }    
}