Java Basics Quick Review with examples

Java Programming Language

• High Level
• Strongly Typed means no automatic type conversions in java like C++
• Case Sensitive
• Successor of c++
• Pure Object Oriented Language

 Hello World Problem in java

class Test{
public static void main(String a[]) {
System.out.println("Hello World");
 }

}

More than one Classes

class Test1{
void print () {
System.out.println("Test class");
}
}
class Test{
public static void main(String a[]) {

Test1 t=new Test1();
t.print();
 }

}

Rule of Thumb: Don't write extra functions in driver class

 Extra function and data in driver class 

class Test{
int sq(int p){
   return p*p;
}
public static void main(String a[]) {
    Test t = new Test();
System.out.println(t.sq(4));
 }

}
..................................
call without object instantiation
..................................

class Test{
static int sq(int p){
   return p*p;
}
public static void main(String a[]) {
System.out.println(sq(4));
 }

}
..................................... 

Math Class Example
class MyMath{
int sq(int p){
 return p*p;
}
int power(int x , int y){
 if (y==0)
    return 1;
 else
    return x * power(x,y-1);
}
}
class Test{
public static void main(String a[]) {
MyMath m= new MyMath();
System.out.println(m.sq(4));
System.out.println(m.power(2,3));
 }
}
.....................................

calling methods without object instantiation

..................................
class MyMath{
static int sq(int p){
 return p*p;
}
static int power(int x, int y){
 if (y==0)
    return 1;
 else
    return x * power(x,y-1);
}
}
class Test{
 public static void main(String a[]) {
 System.out.println(MyMath.sq(4));
 System.out.println(MyMath.power(2,3));
 }
}