Fields/state

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

static final

final

static variables

Variable scope

When to use fields

• If it will be used by the whole class not just a method

  • This depends if the class is a single method class (command pattern)

• It is the state of the instance

• There is only one instance of the object passed into the field which is fixed at compile time

  • If using dependency injection, this implementation can be different at runtime

• You should never use a field to simplify passing data from one method to another method.

• The object of the field will always be used in same way ie call to some instance method to apply some logic

  • Where as the parameter, depending on its state may be used differently

When to use over a method variable or parameters

• Parameters constantly change, when the method is called.

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