Page History

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public class Widget {
  public int total; // Number of elements

  void add() {
    if (total < Integer.MAX_VALUE) {      
      total++;
      // ...
    } else {
      throw new ArithmeticException("Overflow");
    }
  }

  void remove() {  
    if (total > 0) {      
      total--;
      // ...
    } else {
      throw new ArithmeticException("Overflow");
    }
  }
}

Wiki MarkupAs a public data member, {{total}} can be altered by external code independently of the {{add()}} and {{remove()}} methods. It is bad practice to expose fields from a public class \[ [Bloch 2008|AA. References#Bloch 08]\].

Compliant Solution (Private)

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Depending on the required functionality, wrapper methods may retrieve either a reference to the HashMap, a copy of the HashMap, or a value contained by the HashMap. This compliant solution adds a wrapper method to return the value of an element given its index in the HashMap.

Exceptions

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*OBJ01-EX0:* According to Sun's Code Conventions document \ [[Conventions 2009|AA. References#Conventions 09]\]:

One example of appropriate public instance variables is the case where the class is essentially a data structure, with no behavior. In other words, if you would have used a struct instead of a class (if Java supported struct), then it's appropriate to make the class's instance variables public.

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*OBJ01-EX1:* "If a class is package-private or is a {{private}} nested class, there is nothing inherently wrong with exposing its data fields -- – assuming they do an adequate job of describing the abstraction provided by the class. This approach generates less visual clutter than the accessor-method approach, both in the class definition and in the client code that uses it" \[ [Bloch 2008|AA. References#Bloch 08]\]. This exception applies to both mutable and immutable fields.

OBJ01-EX2: Static final fields that contain mathematical constants may be declared public.

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CERT C++ Secure Coding Standard	OOP00-CPP. Declare data members private
MITRE CWE	CWE-766. Critical variable declared public
Secure Coding Guidelines for the Java Programming Language, Version 3.0	Guideline 3-2. Define wrapper methods around modifiable internal state

Bibliography

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[[Bloch 2008AA. References#Bloch 08] ]	Item 13. Minimize the accessibility of classes and members; Item 14. In public classes, use accessor methods, not public fields	]]></ac:plain-text-body></ac:structured-macro>
<ac:structured-macro ac:name="unmigrated-wiki-markup" ac:schema-version="1" ac:macro-id="94d6e1c8-160a-4189-909a-1671e02d72a4"><ac:plain-text-body><![CDATA[	[ [JLS 2005AA. References#JLS 05] ]	[§6.6, Access Control	http://java.sun.com/docs/books/jls/third_edition/html/names.html#6.6]	]]></ac:plain-text-body></ac:structured-macro>	<ac:structured-macro ac:name="unmigrated-wiki-markup" ac:schema-version="1" ac:macro-id="70fdc2b8-4bf8-4363-b2fc-443e45a0f288"><ac:plain-text-body><![CDATA[
[[Long 2005AA. References#Long 05]]	§2.2, Public Fields ]]></ac:plain-text-body></ac:structured-macro>

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OBJ00-J. Limit extensibility of classes and methods with invariants to trusted subclasses only      04. Object Orientation (OBJ)