Java Methods & Static blocks - Class 6

Java methods

Java methods tutorial: Java program consists of one or more classes and a class may contain method(s). A class can do very little without methods. In this tutorial we will learn about Java methods. Methods are known as functions in C and C++ programming languages. A method has a name and return type. Main method is a must in a Java program as execution begins from it.

Syntax of methods

"Access specifier" "Keyword(s)" "return type" methodName(List of arguments) {
// Body of method
}
Access specifier can be public or private which decides whether other classes can call a method.
Kewords are used for some special methods such as static or synchronized.
Return type indicate return value which method returns.
Method name is a valid Java identifier name.
Access specifier, Keyword and arguments are optional.
Examples of methods declaration:
public static void main(String[] args);
void myMethod();
private int maximum();
public synchronized int search(java.lang.Object);

Java Method example program

class Methods {
 
  // Constructor method
 
  Methods() {
    System.out.println("Constructor method is called when an object of it's class is created");
  }
 
  // Main method where program execution begins
 
  public static void main(String[] args) {
    staticMethod();
    Methods object = new Methods();
    object.nonStaticMethod();
  }
 
  // Static method
 
  static void staticMethod() {
    System.out.println("Static method can be called without creating object");
  }
 
  // Non static method
 
  void nonStaticMethod() {
    System.out.println("Non static method must be called by creating an object");
  }
}

Output of program:

Download Methods program class file.

Java methods list

Java has a built in library of many useful classes and there are thousands of methods which can be used in your programs. Just call a method and get your work done :) . You can find list of methods in a class by typing following command on command prompt:
javap package.classname
For example
javap java.lang.String // list all methods and constants of String class.
javap java.math.BigInteger // list constants and methods of BigInteger class in java.math package

Java String methods

String class contains methods which are useful for performing operations on String(s). Below program illustrate how to use inbuilt methods of String class.

Java string class program

class StringMethods
{
  public static void main(String args[])
  {
    int n;
    String s = "Java programming", t = "", u = "";
 
    System.out.println(s);
 
    // Find length of string
 
    n = s.length();
    System.out.println("Number of characters = " + n);
 
    // Replace characters in string
 
    t = s.replace("Java", "C++");
    System.out.println(s);
    System.out.println(t);
 
    // Concatenating string with another string
 
    u = s.concat(" is fun");
    System.out.println(s);
    System.out.println(u);
  }
}

Output of program:

Java static block program

Java programming language offers a block known as static which is executed before main method executes. Below is the simplest example to understand functioning of static block later we see a practical use of static block.

Java static block program

class StaticBlock {
  public static void main(String[] args) {
    System.out.println("Main method is executed.");
  }
 
  static {
    System.out.println("Static block is executed before main method.");
  }
}

Output of program:

Static block can be used to check conditions before execution of main begin, Suppose we have developed an application which runs only on Windows operating system then we need to check what operating system is installed on user machine. In our java code we check what operating system user is using if user is using operating system other than "Windows" then the program terminates.

class StaticBlock {
  public static void main(String[] args) {
    System.out.println("You are using Windows_NT operating system.");
  }
 
  static {
    String os = System.getenv("OS");
    if (os.equals("Windows_NT") != true) {
      System.exit(1);
    }
  }
}

We are using getenv method of System class which returns value of environment variable name of which is passed an as argument to it. Windows_NT is a family of operating systems which includes Windows XP, Vista, 7, 8 and others.
Output of program on Windows 7: