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Method and constructor overloading allows one declaration of two or more methods or constructors with the same name to be invoked, depending on the types of their argumentsbut with different parameter lists. The compiler inspects a each call to an overloaded method or constructor and , using uses the declared types of the method parameters , decides to decide which method to useinvoke. In some cases, however, ambiguity confusion may arise because of the presence of relatively newer new language features such as autoboxing and generics.

Furthermore, methods or constructors with the same parameter types that differ only in their declaration order , are typically not flagged by Java compilers. This Errors can result in errors if when a developer does not fails to consult the documentation at every each use of the a method or constructor. A related pitfall is to associate differing different semantics with each of the overloaded methods or constructors. Defining different semantics sometimes necessitates different orderings of the same method parameters, creating a vicious circle. Consider, for example a , an overloaded getDistance() method whose in which one overloading overloaded method returns the distance traveled from the source while another (with rearranged reordered parameters) returns the uncovered remaining distance to the destination. An implementer Implementers may not fail to realize the difference unless they consult the documentation is consulted at every each use.

Noncompliant Code Example (

...

Constructor)

Constructors cannot be overridden and  and can only be overloaded. This noncompliant code example shows the constructor class Con with three overloadings Con(int, String), Con(String, int) and Con(Integer, String). overloaded constructors:

class Con {
  public Con(int i, String s) { 
    /*/ Initialization Sequence #1
 */ }
  public Con(String s, int i) {
    /*/ Initialization Sequence #2 */
  } 
  public Con(Integer i, String s) {
    /*/ Initialization Sequence #3 
 */ } 
}

Failure to exercise caution while passing arguments to these constructors can create confusion as these overloadings can because calls to these constructors contain the same number of similarly typed actual parameters. Overloading must also be avoided when the overloaded constructors or methods provide inconsistent functionality for arguments distinct semantics for formal parameters of the same types, differing just solely in their declaration order.

Compliant Solution (

...

Constructor)

This compliant solution uses avoids overloading by declaring public static factory methods instead having distinct names in place of the public class constructors.:

public static voidCon ConName1createCon1(int i, String s) { 
  /* Initialization Sequence #1 */ 
}
public static voidCon ConName2createCon2(String s, int i) { 
  /* Initialization Sequence #2 */ 
}
public static voidCon ConName3createCon3(Integer i, String s) {
  /* Initialization Sequence #3 */ 
}

Noncompliant Code Example (

...

Method)

In this noncompliant code example, the InformationLeak OverLoader class holds a HashMap instance and returns a particular record to the caller based on either its key value in the map or the actual mapped value. The getData() method has been overloaded to return the contained data indexed by the key value in the former case. In the latter case, it checks whether a particular record exists before formatting and returning it as a String object. The InformationLeak class inherits from java.util.HashMap and overrides its get() method to provide the checking functionality. This implementation can be extremely confusing to the client who will expect the getData() methods to behave in a similar fashion and not depend on whether an index of the record is specified or the value to be retrieved. A further problem is that, in the presence of autoboxing, an int argument may invoke the undesired overloading for Integer. This can happen if the overloading with the primitive int type is added to a class at a later date. Clients who expect the getData() method to fetch data based on its value will suddenly start invoking the new overloading whenever an int argument is passed and proceed to return the record by index. This happens because a primitive argument becomes more specific in the new version whereas in the old one, autoboxing allows the selection of the method with the Integer type parameter when an int is passed.overloaded getData() methods. One getData() method chooses the record to return on the basis of its key value in the map; the other chooses on the basis of the actual mapped value. 

class BadOverloadingOverLoader extends HashMapHashMap<Integer,Integer> {
  HashMap<Integer,Integer> hm;
  public BadOverloadingOverLoader() {
    hm = new HashMap<Integer, Integer>();
    // SSN records
   hm hm.put(1, 111990000);
    hm.put(2, 222990000);
    hm.put(3, 333990000);  // ssn records	  
  }
  public Integer getData(int i) { // Overloading sequence #1
    return hm.get(i); // get record at position 'i'
  }
  public String getData(Integer i) { // Overloading sequence #2#1
    String s = get(i).toString(); // getGet a particular record
    return (s.substring(0, 3) + "-" + s.substring(3, 5) + "-" + 
            s.substring(5, 9));
	  
  }
  @Override public Integer getgetData(Objectint datai) { // Overloading sequence #2
    return hm.get(i); // Get record at position 'i'
  }
  // Checks whether the ssn exists
  @Override public Integer get(Object data) {
    // SecurityManagerCheck()

    for (Map.Entry<Integer, Integer> entry : hm.entrySet()) {
      if(entry.getValue().compareToequals((Integerdata)data) == 0){
        return entry.getValue();  // Exists 
      }
    }
    return null;
  }
  public static void main(String[] args) {
    BadOverloadingOverLoader bo = new BadOverloadingOverLoader();
    // Get record at index '3'
    System.out.println(bo.getData(3));
    // Get record atcontaining indexdata '3111990000'
     System.out.println(bo.getData((Integer)111990000)); // Get record containing data '111990000'
  }
}

Although the client programmer might eventually deduce such behavior, other cases such as with the {{List}} interface may go unnoticed as Bloch \[[Bloch 2008|AA. Bibliography#Bloch 08]\] describes:

For purposes of overload resolution, the signatures of the getData() methods differ only in the static type of their formal parameters. The OverLoader class inherits from java.util.HashMap and overrides its get() method to provide the checking functionality. This implementation can be extremely confusing to the client who expects both getData() methods to behave in a similar fashion and not depend on whether an index of the record or the value to be retrieved is specified.

Although the client programmer might eventually deduce such behavior, other cases, such as with the List interface, may go unnoticed, as Joshua Bloch [Bloch 2008] describes:

The ... the List<E> interface has two overloadings of the remove method: remove(E) and remove(int). Prior to release 1.5 when it was "generified," , the List interface had a remove(Object) method in place of remove(E), and the corresponding parameter types, Object and int, were radically different. But in the presence of generics and autoboxing, the two parameter types are no longer radically different.

Consequently, a client programmer may not fail to realize that the wrong element has been removed from the list.

A further problem is that in the presence of autoboxing, adding a new overloaded method definition can break previously working client code. This can happen when a new overloaded method with a more specific type is added to an API whose methods used less specific types in earlier versions. For example, if an earlier version of the OverLoader class provided only the getData(Integer) method, the client could correctly invoke this method by passing a parameter of type int; the result would be selected on the basis of its value because the int parameter would be autoboxed to Integer. Subsequently, when the getData(int) method is added, the compiler resolves all calls whose parameter is of type int to invoke the new getData(int) method, thereby changing their semantics and potentially breaking previously correct code. The compiler is entirely correct in such cases; the actual problem is an incompatible change to the API.

Compliant Solution (

...

Method)

Naming the two related methods differently eliminates both the overloading and the confusion.

public Integer getDataByIndex(int i) { 
  //* noNo longer overloaded */ 
}

public String getDataByValue(Integer i) {
  /*/ noNo longer overloaded */ 
}

...

Applicability

Ambiguous or confusing uses of overloading can lead to unexpected results.

...

Automated Detection

Automated Detection

TODO

Related Vulnerabilities

Search for vulnerabilities resulting from the violation of this guideline on the CERT website.

Bibliography

\[[API 2006|AA. Bibliography#API 06]\] [Interface Collection|http://java.sun.com/j2se/1.4.2/docs/api/java/util/Collection.html]
\[[Bloch 2008|AA. Bibliography#Bloch 08]\] Item 41: Use overloading judiciously

Bibliography

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Image Added Image Added Image Added05. Methods (MET)      05. Methods (MET)      MET01-J. Validate method parameters