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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 MSC07-J. Prevent 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="88821e1c28c58916-d17b9424-418342da-b870a08a-04fc4f2ad84bd34d0ad53e2b"><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="ffd77c829a9d325d-4f85a84d-453c47d7-bcfdb021-7b84dc0f82b2c379e95c94ba"><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="8c6c46b396939c9e-38fa0ac3-43b34076-b48eab08-c412b4856ef75b06c089ef5c"><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="789512d4a8d858b0-9c87e16e-45914370-b70b961e-210d2798c29ffc3d48c2282b"><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="cb99620cf598fc5e-36516ca5-47c14d5f-b0188cde-f55ab44f0924a2cc354c5380"><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="3c72e490889c766c-a2905b2f-40f3469c-a14d896d-5a501518f78736c1d8bc356e"><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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