METHODS:
A Java method is a collection of statements that are grouped together
to perform an operation. When you call the System.out.println method,
for example, the system actually executes several statements in order to
display a message on the console.
Now you will learn how to create your own methods with or without
return values, invoke a method with or without parameters, overload
methods using the same names, and apply method abstraction in the
program design.
Creating Method:
Considering the following example to explain the syntax of a method:
public static int funcName(int a, int b) {
// body
}
Here,
- public static : modifier.
- int: return type
- funcName: function name
- a, b: formal parameters
- int a, int b: list of parameters
Methods are also known as Procedures or Functions:
- Procedures: They don't return any value.
- Functions: They return value.
Method definition consists of a method header and a method body. The same is shown below:
modifier returnType nameOfMethod (Parameter List) {
// method body
}
The syntax shown above includes:
- modifier: It defines the access type of the method and it is optional to use.
- returnType: Method may return a value.
- nameOfMethod: This is the method name. The method signature consists of the method name and the parameter list.
- Parameter List: The list of parameters, it is the type,
order, and number of parameters of a method. These are optional, method
may contain zero parameters.
- method body: The method body defines what the method does with statements.
Example:
Here is the source code of the above defined method called max().
This method takes two parameters num1 and num2 and returns the maximum
between the two:
/** the snippet returns the minimum between two numbers */
public static int minFunction(int n1, int n2) {
int min;
if (n1 > n2)
min = n2;
else
min = n1;
return min;
}
Method Calling:
For using a method, it should be called. There are two ways in which a
method is called i.e. method returns a value or returning nothing (no
return value).
The process of method calling is simple. When a program invokes a
method, the program control gets transferred to the called method. This
called method then returns control to the caller in two conditions,
when:
- return statement is executed.
- reaches the method ending closing brace.
The methods returning void is considered as call to a statement. Lets consider an example:
System.out.println("This is tutorialspoint.com!");
The method returning value can be understood by the following example:
int result = sum(6, 9);
Example:
Following is the example to demonstrate how to define a method and how to call it:
public class ExampleMinNumber{
public static void main(String[] args) {
int a = 11;
int b = 6;
int c = minFunction(a, b);
System.out.println("Minimum Value = " + c);
}
/** returns the minimum of two numbers */
public static int minFunction(int n1, int n2) {
int min;
if (n1 > n2)
min = n2;
else
min = n1;
return min;
}
}
This would produce the following result:
Minimum value = 6
The void Keyword:
The void keyword allows us to create methods which do not return a
value. Here, in the following example we're considering a void method
methodRankPoints. This method is a void method which does not return any value. Call to a void method must be a statement i.e.
methodRankPoints(255.7);. It is a Java statement which ends with a semicolon as shown below.
Example:
public class ExampleVoid {
public static void main(String[] args) {
methodRankPoints(255.7);
}
public static void methodRankPoints(double points) {
if (points >= 202.5) {
System.out.println("Rank:A1");
}
else if (points >= 122.4) {
System.out.println("Rank:A2");
}
else {
System.out.println("Rank:A3");
}
}
}
This would produce the following result:
Rank:A1
Passing Parameters by Value:
While working under calling process, arguments is to be passed.
These should be in the same order as their respective parameters in the
method specification. Parameters can be passed by value or by reference.
Passing Parameters by Value means calling a method with a parameter. Through this the argument value is passed to the parameter.
Example:
The following program shows an example of passing parameter by value.
The values of the arguments remains the same even after the method
invocation.
public class swappingExample {
public static void main(String[] args) {
int a = 30;
int b = 45;
System.out.println("Before swapping, a = " +
a + " and b = " + b);
// Invoke the swap method
swapFunction(a, b);
System.out.println("\n**Now, Before and After swapping values will be same here**:");
System.out.println("After swapping, a = " +
a + " and b is " + b);
}
public static void swapFunction(int a, int b) {
System.out.println("Before swapping(Inside), a = " + a
+ " b = " + b);
// Swap n1 with n2
int c = a;
a = b;
b = c;
System.out.println("After swapping(Inside), a = " + a
+ " b = " + b);
}
}
This would produce the following result:
Before swapping, a = 30 and b = 45
Before swapping(Inside), a = 30 b = 45
After swapping(Inside), a = 45 b = 30
**Now, Before and After swapping values will be same here**:
After swapping, a = 30 and b is 45
Method Overloading:
When a class has two or more methods by same name but different
parameters, it is known as method overloading. It is different from
overriding. In overriding a method has same method name, type, number of
parameters etc.
Lets consider the example shown before for finding minimum numbers of
integer type. If, lets say we want to find minimum number of double
type. Then the concept of Overloading will be introduced to create two
or more methods with the same name but different parameters.
The below example explains the same:
public class ExampleOverloading{
public static void main(String[] args) {
int a = 11;
int b = 6;
double c = 7.3;
double d = 9.4;
int result1 = minFunction(a, b);
// same function name with different parameters
double result2 = minFunction(c, d);
System.out.println("Minimum Value = " + result1);
System.out.println("Minimum Value = " + result2);
}
// for integer
public static int minFunction(int n1, int n2) {
int min;
if (n1 > n2)
min = n2;
else
min = n1;
return min;
}
// for double
public static double minFunction(double n1, double n2) {
double min;
if (n1 > n2)
min = n2;
else
min = n1;
return min;
}
}
This would produce the following result:
Minimum Value = 6
Minimum Value = 7.3
Overloading methods makes program readable. Here, two methods are
given same name but with different parameters. The minimum number from
integer and double types is the result.
Using Command-Line Arguments:
Sometimes you will want to pass information into a program when you
run it. This is accomplished by passing command-line arguments to main(
).
A command-line argument is the information that directly follows the
program's name on the command line when it is executed. To access the
command-line arguments inside a Java program is quite easy.they are
stored as strings in the String array passed to main( ).
Example:
The following program displays all of the command-line arguments that it is called with:
public class CommandLine {
public static void main(String args[]){
for(int i=0; i<args.length; i++){
System.out.println("args[" + i + "]: " +
args[i]);
}
}
}
Try executing this program as shown here:
java CommandLine this is a command line 200 -100
This would produce the following result:
args[0]: this
args[1]: is
args[2]: a
args[3]: command
args[4]: line
args[5]: 200
args[6]: -100
The Constructors:
A constructor initializes an object when it is created. It has the
same name as its class and is syntactically similar to a method.
However, constructors have no explicit return type.
Typically, you will use a constructor to give initial values to the
instance variables defined by the class, or to perform any other startup
procedures required to create a fully formed object.
All classes have constructors, whether you define one or not, because
Java automatically provides a default constructor that initializes all
member variables to zero. However, once you define your own constructor,
the default constructor is no longer used.
Example:
Here is a simple example that uses a constructor:
// A simple constructor.
class MyClass {
int x;
// Following is the constructor
MyClass() {
x = 10;
}
}
You would call constructor to initialize objects as follows:
public class ConsDemo {
public static void main(String args[]) {
MyClass t1 = new MyClass();
MyClass t2 = new MyClass();
System.out.println(t1.x + " " + t2.x);
}
}
Most often, you will need a constructor that accepts one or more
parameters. Parameters are added to a constructor in the same way that
they are added to a method, just declare them inside the parentheses
after the constructor's name.
Example:
Here is a simple example that uses a constructor:
// A simple constructor.
class MyClass {
int x;
// Following is the constructor
MyClass(int i ) {
x = i;
}
}
You would call constructor to initialize objects as follows:
public class ConsDemo {
public static void main(String args[]) {
MyClass t1 = new MyClass( 10 );
MyClass t2 = new MyClass( 20 );
System.out.println(t1.x + " " + t2.x);
}
}
This would produce the following result:
10 20
Variable Arguments(var-args):
JDK 1.5 enables you to pass a variable number of arguments of the
same type to a method. The parameter in the method is declared as
follows:
typeName... parameterName
In the method declaration, you specify the type followed by an
ellipsis (...) Only one variable-length parameter may be specified in a
method, and this parameter must be the last parameter. Any regular
parameters must precede it.
Example:
public class VarargsDemo {
public static void main(String args[]) {
// Call method with variable args
printMax(34, 3, 3, 2, 56.5);
printMax(new double[]{1, 2, 3});
}
public static void printMax( double... numbers) {
if (numbers.length == 0) {
System.out.println("No argument passed");
return;
}
double result = numbers[0];
for (int i = 1; i < numbers.length; i++)
if (numbers[i] > result)
result = numbers[i];
System.out.println("The max value is " + result);
}
}
This would produce the following result:
The max value is 56.5
The max value is 3.0
The finalize( ) Method:
It is possible to define a method that will be called just before an
object's final destruction by the garbage collector. This method is
called
finalize( ), and it can be used to ensure that an object terminates cleanly.
For example, you might use finalize( ) to make sure that an open file owned by that object is closed.
To add a finalizer to a class, you simply define the finalize( )
method. The Java runtime calls that method whenever it is about to
recycle an object of that class.
Inside the finalize( ) method, you will specify those actions that must be performed before an object is destroyed.
The finalize( ) method has this general form:
protected void finalize( )
{
// finalization code here
}
Here, the keyword protected is a specifier that prevents access to finalize( ) by code defined outside its class.
This means that you cannot know when or even if finalize( ) will be
executed. For example, if your program ends before garbage collection
occurs, finalize( ) will not execute.
