1. Scope of variables class scopeofvars {
public static void main(String args[]) {
int x; // known to all code within main
x = 10;
if(x == 10) { // start new scope
int y = 20; // known only to this block
// x and y both known here.
System.out.println("x and y: " + x + " " + y);
x = y * 2; }
// y = 100; // Error! y not known here
// x is still known here.
System.out.println("x is " + x);

2. Scope of variables contd
class lifetime1 {
public static void main(String args[]) {
int x;
for(x = 0; x < 3; x++) {
int y = -1; // y is initialized each time block is entered
System.out.println("y is: " + y); // this always prints -1
y = 100;
System.out.println("y is now: " + y); }

3. Scope of variables contd
class lifetime2 {
public static void main(String args[]) {
int count;
for(count = 0; count < 10; count = count+1) {
System.out.println("This is count: " + count);
int count; // illegal!!!
for(count = 0; count < 2; count++)
System.out.println("This program is in error!"); }

4. Methods in problem solving
Often we think of solving a large problem in parts
Computing the number of digits in n! involves two major steps: computing k=n! and computing the number of digits in k
So I can have two “procedures”, one computes n! and the other computes the number of digits in it
Such procedures are called methods
These are just like functions
A method may or may not produce a value
The type of the produced value determines the “return type” of a method

5. Return and parameter type
Can be int, float, String, double, char, or void
We have seen one method so far: main
It does not produce any value: void
public static void PrintMyName () {
System.out.println(“Tintin”); }
Every method must be a part of a class

6. PrintMyName class anExample { public static void main (String arg[]) {
PrintMyName(); // Method call }
public static void PrintMyName () {
// Method declaration
System.out.println(“Tintin”);

7. Method parameters Methods can have parameters also class anExample {
Just like functions
class anExample {
public static void main (String arg[]) {
String myName = “Tintin”;
PrintMyName(myName); }
public static void PrintMyName (String s) {
System.out.println(s);