Method Overloading (function overloading) in Java

By: Abinaya  

In Java it is possible to define two or more methods within the same class that share the same name, as long as their parameter declarations are different. When this is the case, the methods are said to be overloaded, and the process is referred to as method overloading. Method overloading is one of the ways that Java implements polymorphism.

If you have never used a language that allows the overloading of methods, then the concept may seem strange at first. But as you will see, method overloading is one of Java's most exciting and useful features. When an overloaded method is invoked, Java uses the type and/or number of arguments as its guide to determine which version of the overloaded method to actually call. Thus,
overloaded methods must differ in the type and/or number of their parameters. While overloaded methods may have different return types, the return type alone is insufficient to distinguish two versions of a method. When Java encounters a call to an overloaded method, it simply executes the version of the method whose parameters match the arguments used in the call. Here is a simple example that illustrates method overloading:

// Demonstrate method overloading.
class OverloadDemo {
void test() {
System.out.println("No parameters");
// Overload test for one integer parameter.
void test(int a) {
System.out.println("a: " + a);
// Overload test for two integer parameters.
void test(int a, int b) {
System.out.println("a and b: " + a + " " + b);
// overload test for a double parameter
double test(double a) {
System.out.println("double a: " + a);
return a*a;
class Overload {
public static void main(String args[]) {
OverloadDemo ob = new OverloadDemo();
double result;
// call all versions of test()
ob.test(10, 20);
result = ob.test(123.2);
System.out.println("Result of ob.test(123.2): " + result);

This program generates the following output:

No parameters
a: 10
a and b: 10 20
double a: 123.2
Result of ob.test(123.2): 15178.24

As you can see, test( ) is overloaded four times. The first version takes no parameters, the second takes one integer parameter, the third takes two integer parameters, and the fourth takes one double parameter. The fact that the fourth version of test( ) also returns a value is of no consequence relative to overloading, since return types do not play a role in overload resolution.

When an overloaded method is called, Java looks for a match between the arguments used to call the method and the method's parameters. However, this match need not always be exact. In some cases Java's automatic type conversions can play a role in overload resolution. For example, consider the following program:

// Automatic type conversions apply to overloading.
class OverloadDemo {
void test() {
System.out.println("No parameters");
// Overload test for two integer parameters.
void test(int a, int b) {
System.out.println("a and b: " + a + " " + b);
// overload test for a double parameter
void test(double a) {
System.out.println("Inside test(double) a: " + a);
class Overload {
public static void main(String args[]) {
OverloadDemo ob = new OverloadDemo();
int i = 88;
ob.test(10, 20);
ob.test(i); // this will invoke test(double)
ob.test(123.2); // this will invoke test(double)

This program generates the following output:

No parameters
a and b: 10 20
Inside test(double) a: 88
Inside test(double) a: 123.2

As you can see, this version of OverloadDemo does not define test(int). Therefore, when test( ) is called with an integer argument inside Overload, no matching method is found. However, Java can automatically convert an integer into a double, and this conversion can be used to resolve the call. Therefore, after test(int) is not found, Java elevates i to double and then calls test(double). Of course, if test(int) had been defined, it would have been called instead. Java will employ its automatic type conversions only if no exact match is found.

Method overloading supports polymorphism because it is one way that Java implements the "one interface, multiple methods" paradigm. To understand how, consider the following. In languages that do not support method overloading, each method must be given a unique name. However, frequently you will want to implement essentially the same method for different types of data. Consider the absolute value function. In languages that do not support overloading, there are usually three or more versions of this function, each with a slightly different name. For instance, in C, the function abs( )
returns the absolute value of an integer, labs( ) returns the absolute value of a long integer, and fabs() returns the absolute value of a floating-point value. Since C does not support overloading, each function has to have its own name, even though all three functions do essentially the same thing. This makes the situation more complex, conceptually, than it actually is. Although the underlying concept of each function is the same, you still have three names to remember. This situation does not occur in Java, because each absolute value method can use the same name. Indeed, Java's standard class library includes an absolute value method, called abs( ). This method is overloaded
by Java's Math class to handle all numeric types. Java determines which version of abs() to call based upon the type of argument.

The value of overloading is that it allows related methods to be accessed by use of a common name. Thus, the name abs represents the general action which is being performed. It is left to the compiler to choose the right specific version for a particular circumstance. You, the programmer, need only remember the general operation being performed. Through the application of polymorphism, several names have been reduced to one. Although this example is fairly simple, if you expand the concept, you can see how overloading can help you manage greater complexity.

When you overload a method, each version of that method can perform any activity you desire. There is no rule stating that overloaded methods must relate to one another. However, from a stylistic point of view, method overloading implies a relationship. Thus, while you can use the same name to overload unrelated methods, you should not. For example, you could use the name sqr to create methods that return the square of an integer and the square root of a floating-point value. But these two operations are fundamentally different. Applying method overloading in this manner defeats its original purpose. In practice, you should only overload closely related operations.

This is an extract from the book Java: the complete reference. By Herbert Schildt

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by- shiv at 2010-11-26 11:51:20

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View Tutorial          By: manogna at 2010-10-13 02:24:06

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View Tutorial          By: mahesh at 2010-10-05 00:46:11

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View Tutorial          By: Rachana at 2010-10-03 06:10:32

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View Tutorial          By: jasim Khalid almurakh meherbani at 2010-09-20 03:14:25

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View Tutorial          By: Anup at 2010-09-16 12:11:25

101. vry nice example....thanx..
View Tutorial          By: rekha at 2010-09-14 11:55:38

102. what are the disadvantage of using the function overloading
View Tutorial          By: rajesh at 2010-09-12 03:55:25

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View Tutorial          By: Deepak at 2010-09-10 10:58:22

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View Tutorial          By: sam at 2010-08-28 01:50:51

105. It's helpful to me.. to understand stand clear picture of method overloading concept... with good ex
View Tutorial          By: Ansari at 2010-08-18 10:22:54

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View Tutorial          By: V.Ranjith kumar at 2010-08-12 06:13:03

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View Tutorial          By: Som2ie at 2010-08-02 05:07:37

108. very nice program but more info require
View Tutorial          By: pradeep at 2010-07-15 01:11:37

109. what about the access modifiers, while talking about the method overloading in java?
View Tutorial          By: Seetha at 2010-06-04 01:14:02

110. very simple to understand
View Tutorial          By: chermaraja at 2010-05-26 00:00:38

111. very simple to understand
View Tutorial          By: chermaraja at 2010-05-26 00:00:05

112. thankssss to prograem
View Tutorial          By: maha at 2010-05-21 05:14:36

113. return type doesn't influence the overloading. Only parameter type and number of parameter need to b
View Tutorial          By: Shekhar at 2010-05-17 01:22:04

114. very simple and nice examples for begineer...
View Tutorial          By: sarhand at 2010-04-21 00:57:23

115. @dodo : Overloading is only for parameter types and the return type wont influence the overloading..
View Tutorial          By: sundar at 2010-04-19 02:44:23

116. if return type is different but parameters same does overloading occurs??????????????????
View Tutorial          By: dodo at 2010-04-08 23:08:58

117. thank you..........
View Tutorial          By: ravi at 2010-01-29 23:27:39

118. Sorry, please disregard my previous comment... Thank you for the good discussion! :) God bless! :)
View Tutorial          By: choco at 2010-01-03 02:21:09

119. Thank you! :) But I have a question, why is that the value of result in the first code is 15178.24?
View Tutorial          By: choco at 2010-01-03 02:16:18

120. it's very good to understand...and it is helpful for learners...who not understand about overloadin
View Tutorial          By: Rakesh at 2009-12-26 00:14:59

121. it is nice but please give simple example like area of rectangel
View Tutorial          By: red at 2009-12-03 23:07:37

122. This example is very clear. I cleared my concept of overloading here. Thanks
View Tutorial          By: sukanta at 2009-10-20 06:08:50

123. Thanks this page is very useful for me and now I know something I missed in my class about method ov
View Tutorial          By: Yee Wai Wyne at 2009-10-18 23:03:41

124. thaanks alot
View Tutorial          By: vinaykumar at 2009-09-24 04:10:06

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View Tutorial          By: gurav gupta at 2009-09-24 00:20:15

126. Great Thanks
View Tutorial          By: seedimani at 2009-09-16 01:27:26

127. thanks this material is very helpful for me
View Tutorial          By: Anonymous at 2009-05-09 08:04:31

128. Is operator overloading possible in java??????
View Tutorial          By: rishi at 2008-11-01 23:55:55

129. plz explain in
simple way like give easiy examples but other wise thank for give me

View Tutorial          By: mani at 2008-10-20 01:32:50

130. good job
View Tutorial          By: gopi at 2008-07-01 02:02:48

131. Great! Thanks!
View Tutorial          By: sciarp at 2008-05-11 05:04:17

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