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METHODS IN JAVA
A class represent the properties and behabiour of an object. An methods represent these behaviours.
Methods in Java are blocks of code with
a name
a paranthesis that can accept zero or more parameters
can optionally return a value.
has a body block enclosed within two curly braces {}.
Signature and body of a method
The first line of a method with its access specifier (who all can access), return type (what will this method return to its caller), name and the paranthesis with zero or more parameters, is called the method signature. The body follows the signature starting with { and ending with }.
Example: The main method When you execute a Java class (using java command) in console, JVM first calls a predefined method called main with a particular signature and then we can start calling other methods from there.
public static void main(String[] args)
{
//method body
}
Explanation of various terms used:
public - is the access specifier that tells how visible the method is within and outside the class. Possible values are public, private, protected and default (no access modifier).
static - this is a static method, not an instance method.
void - return type. void means nothing is returned.
main - name of the method.
args - A String array to accept command line arguments.
Rules for declaring a method
It is mandatory to specify return type while declaring a method; if nothing is returned, specify it as void. We should return a value compatible with the return type and do any casting if required. If you have specified the return type as void you can either omit the return statement or simply have the return statement as return;. We can have any primitive type like int, float etc or any reference type (class or interface) as the return type.
Like variables, methods can also be static or instance. Static methods will have a static keyword in its signature line (as in the case of main method).
From a static context (e.g. static method) you cannot access non-static members (e.g. non-static variables or methods). However, from non-static context (e.g. non-static method), you can access static members (e.g. static variables or methods).
Invoking methods
Methods are not automatically invoked like initialization blocks and constructors, but need to be invoked explicitely from within the code; only exception is the main method which is invoked automatically by the JVM.
Invocation is similar to the usage of instance and static variables, but need to pass any required arguments.
o For instance if your method signature says add(int a, int b), you need to invoke it as add(1,2) or add(x,y) where x and y are integers.
Using object reference for instance methods Instance methods are invoked using an object reference.
Example: An instance method with signature public void myMethod(int i) can be invoked as:
MyClass mc = new MyClass();
mc.myMethod(5);
Saving the return value after calling a method
int var1=0;
int var2;
//inner block within method
{ int var3=0; System.out.println("var1="+var1); System.out.println("var3="+var3); } System.out.println("var1="+var1);
/* Below line won't compile as var2 is not initialized. */
//System.out.println("var2="+var2);
/* Below line won't compile as var3 is not visible outside the block in which it was defined. */
//System.out.println("var3="+var3);
}
Source : http://javajee.com/methods-in-java
