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bgColor	#FFcccc

public class SensitiveClass extends Exception {
  public static final SensitiveClass INSTANCE = new SensitiveClass();
  private SensitiveClass() {
    // Perform security checks and parameter validation
  }

  protected int printBalance() {
    int balance = 1000;
    return balance;
  }
}

class Malicious {
  public static void main(String[] args) {
    SensitiveClass sc = (SensitiveClass) deepCopy(SensitiveClass.INSTANCE);
    System.out.println(sc == SensitiveClass.INSTANCE);  // Prints false; indicates new instance
    System.out.println("Balance = " + sc.printBalance());
  }

  // This method should not be used in production quality code
  static public Object deepCopy(Object obj) {
    try {
      ByteArrayOutputStream bos = new ByteArrayOutputStream();
      new ObjectOutputStream(bos).writeObject(obj);
      ByteArrayInputStream bin = new ByteArrayInputStream(bos.toByteArray());
      return new ObjectInputStream(bin).readObject();
    } catch (Exception e) { 
      throw new IllegalArgumentException(e);
    }
  }
}

See rule MSC11-J. Address the shortcomings of the Singleton design patternPrevent multiple instantiations of singleton objects for more information on singletons.

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<ac:structured-macro ac:name="unmigrated-wiki-markup" ac:schema-version="1" ac:macro-id="8251010cbb7ede0e-59c1cd2b-44304a9d-824aa8ee-92e727fb96244427930cc543"><ac:plain-text-body><![CDATA[	[[Bloch 2001	AA. Bibliography#Bloch 01]]	Item 1: Enforce the singleton property with a private constructor	]]></ac:plain-text-body></ac:structured-macro>
<ac:structured-macro ac:name="unmigrated-wiki-markup" ac:schema-version="1" ac:macro-id="34f38d599e55636c-b60c7161-4ce04728-a3fab324-94d02e03ee5756dd59fef9cb"><ac:plain-text-body><![CDATA[	[[Greanier 2000	AA. Bibliography#Greanier 00]]	[Discover the secrets of the Java Serialization API	http://java.sun.com/developer/technicalArticles/Programming/serialization/]	]]></ac:plain-text-body></ac:structured-macro>
<ac:structured-macro ac:name="unmigrated-wiki-markup" ac:schema-version="1" ac:macro-id="f6f4e639f51d0b40-bccc04d4-479546bf-b7b69a95-c60446b12ac564c8f02fb8a9"><ac:plain-text-body><![CDATA[	[[Harold 1999	AA. Bibliography#Harold 99]]		]]></ac:plain-text-body></ac:structured-macro>
<ac:structured-macro ac:name="unmigrated-wiki-markup" ac:schema-version="1" ac:macro-id="8690b96e2846358f-80c89006-4b5548e3-a67aa29e-93940efb5dcac576002acf98"><ac:plain-text-body><![CDATA[	[[JLS 2005	AA. Bibliography#JLS 05]]	[Transient modifier	http://java.sun.com/docs/books/jls/third_edition/html/classes.html#37020]	]]></ac:plain-text-body></ac:structured-macro>
<ac:structured-macro ac:name="unmigrated-wiki-markup" ac:schema-version="1" ac:macro-id="7db5d109233b669f-37da5a07-4a864746-a438ab66-9782c0837cf91e9fea4dc8eb"><ac:plain-text-body><![CDATA[	[[Long 2005	AA. Bibliography#Long 05]]	Section 2.4, Serialization	]]></ac:plain-text-body></ac:structured-macro>
<ac:structured-macro ac:name="unmigrated-wiki-markup" ac:schema-version="1" ac:macro-id="6c1905abfa4aef47-5b84880f-489e47ac-badeb31c-b71e3d58c1848d3ed49f2008"><ac:plain-text-body><![CDATA[	[[Sun 2006	AA. Bibliography#Sun 06]]	"Serialization specification: A.4 Preventing Serialization of Sensitive Data"	]]></ac:plain-text-body></ac:structured-macro>

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