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

When referring to internal private variables of Java POJOs that have getters/setters, I've used the following terms:

• field
• variable
• attribute
• property

Is there any difference between the above? If so, what is the correct term to use? Is there a different term to use when this entity is persisted?

Solution 1:

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

• field

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

• property

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

• attribute

  • Not listed in the above glossary

• 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.

Solution 2:

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 :)

Solution 3:

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.

Solution 4:

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)