Basic Java Programs :
This keyword :
// This keyword is used to refer current class instance variables
// This keyword is used to call current methods and constrcutors
class ThisKeyword {
int id ; // These are called instance variables
String name ;
String company ;
ThisKeyword() {
System.out.println("this is default constrcutor");
}
ThisKeyword(int id, String name, String company) {
this(); // This should be first line inside another constructor
id =id;
name = name;
company = company;
System.out.println("inside the method id is "+id+ "name is "+name+" company is "+company);
this.displayinfo();
}
void displayinfo() {
System.out.println("id is "+id+ "name is "+name+" company is "+company);
}
void withThisKeyword(int id, String name, String company) {
this.id =id;
this.name = name;
this.company = company;
System.out.println("id is "+id+ "name is "+name+" company is "+company);
}
public static void main(String[] args) {
ThisKeyword thisObj = new ThisKeyword(23, "venkat", "abcd");
thisObj.displayinfo();
//thisObj.withoutThisKeyword(23, "venkat", "abcd");
thisObj.withThisKeyword(23, "venkat", "abcd");
thisObj.displayinfo();
}
}
output :
this is default constrcutor
inside the method id is 23name is venkat company is abcd
id is 0name is null company is null
id is 0name is null company is null
id is 23name is venkat company is abcd
id is 23name is venkat company is abcd
Static Keyword and Static Method :
// Static keyword belongs to the class rather than instance of the class
// Static variable belongs to all the objects of the class
// It is used to save memory
// Static method belong to the class rather than pbject of the class
// Static method can be called using class name
class StaticVariableMethodClass {
int id ;
String name ;
static String company = "abcd"; // will create memory only once
static int n1=0;
int n2=0;
void display(int i, String s) {
System.out.println("id is "+i+" name is "+s+" company is " +company) ;
}
void staticvar() {
n1++; // If any object changes the value of the static variable, it will retain its value.
n2++;
System.out.println("static n1 is "+n1) ;
System.out.println("non static n2 is "+n2) ;
}
static void changeStaticvar()
{
company = "xyz";
System.out.println("static method static var " +company) ;
}
void changeStaticvar1()
{
company = "fgh";
System.out.println("non static method can change the value of static var " +company) ;
}
public static void main(String[] args) {
StaticVariableMethodClass s1 = new StaticVariableMethodClass();
StaticVariableMethodClass s2 = new StaticVariableMethodClass();
s1.display(5, "jai");
s1.staticvar();
s2.staticvar();
StaticVariableMethodClass.changeStaticvar();
StaticVariableMethodClass s3 = new StaticVariableMethodClass();
s3.changeStaticvar1();
}
}
Output:
id is 5 name is jai company is abcd
static n1 is 1
non static n2 is 1
static n1 is 2
non static n2 is 1
static method static var xyz
non static method can change the value of static var fgh
Constructor :
// Constructor is a block codes similar to the method.
// It is called when an instance of the class is created.
// Constructors can be overloaded like methods
// Constructor does not have any return type
class ConstructorTest {
int id ;
String name ;
String college;
ConstructorTest() {
System.out.println("This is default constrcutor which has no params");
}
ConstructorTest(int i, String s) {
id = i;
name = s;
System.out.println("id is : "+i+" name is: "+name);
}
ConstructorTest(int i, String s, String c) {
id = i;
name = s;
college = c;
System.out.println("id is : "+i+" name is: "+name+ " college is: "+college);
}
public static void main(String[] args) {
ConstructorTest obj1 = new ConstructorTest(); // default constructor
ConstructorTest obj2 = new ConstructorTest(12, "venkat"); // parameterrized constructor
ConstructorTest obj3 = new ConstructorTest(12, "venkat", "abcd");
}
}
Class and Object :
// Object is an entity which has state and behaviour
// Class is collection of objects , it is a template or logical entity
class ClassAndObject {
int id ;
String name ;
void display(int i, String s) {
id = i;
name = s;
System.out.println("id is : "+i+" name is: "+name);
}
public static void main(String[] args) {
ClassAndObject obj = new ClassAndObject();
obj.display(8, "jaivardhan");
obj.display(9, "havish") ;
}
}
output :
This is default constrcutor which has no params
id is : 12 name is: venkat
id is : 12 name is: venkat college is: abcd
Basic Java Programs
class JavaPrograms {
void palindrome(int n) {
int original = n;
int p= 0;
while(n!=0) {
int r = n%10; // 123 - 3. 12- 2
p = p*10 + r ; // 30
n = n/10;
}
if(p==original) {
System.out.println("the given number "+original+ " is palindrome");
}
else {
System.out.println("the given number "+original+" is not a palindrome");
}
}
void palindromeString(String s) {
String rev = "";
for(int i=s.length()-1;i>=0;i--) {
rev = rev + s.charAt(i);
}
System.out.println("after reverse selenium is : " +rev);
if(rev.equals(s)) {
System.out.println("the given string "+s+ " is palindrome");
}
else {
System.out.println("the given string "+s+" is not a palindrome");
}
}
void findMaximumNumber(int a[]) {
int max = a[0];
for(int i=1; i<a.length; i++) {
if(max<a[i])
max=a[i];
}
System.out.println("maximum number is : " +max);
}
void findSmallestNumber(int a[]) {
int min = a[0];
for(int i=1; i<a.length; i++) {
if(min>a[i])
min=a[i];
}
System.out.println("smallest number is : " +min);
}
void swap(int a, int b) {
a = a+b ; // 20+30 = 50
b = a-b; // 50-30 = 20
a = a-b; // 50-20 = 30
System.out.println("after swap a = "+a+" and b = "+b);
}
int factorial(int n) {
int fact =1 ;
for(int i=2; i<=n; i++) {
fact = fact * i;
}
return fact;
}
public static void main(String[] args) {
JavaPrograms jp = new JavaPrograms();
System.out.println("factorial value of 5 is : " + jp.factorial(5));
jp.swap(20,30);
int a[] = {34, 45, 12, 67, 54};
jp.findSmallestNumber(a);
jp.findMaximumNumber(a);
jp.palindromeString("selenium");
jp.palindromeString("malayalam");
jp.palindrome(1221);
jp.palindrome(1234);
}
}
factorial value of 5 is : 120
after swap a = 30 and b = 20
smallest number is : 12
maximum number is : 67
after reverse selenium is : muineles
the given string selenium is not a palindrome
after reverse selenium is : malayalam
the given string malayalam is palindrome
the given number 1221 is palindrome
the given number 1234 is not a palindrome
Java - String, StringBuffer and StringBuilder
class HelloWorld {
public static void main(String[] args) {
String s1 = "hello"; // Strings are immuitable
String s2 = "hello"; // s1 and s2 points to the same reference
s1.concat("world"); // s1 does not change because string mutable
System.out.println("string s1 "+ s1);
s1.concat("world");
System.out.println("string s1 after contact: "+ s1);
if(s1==s2) {
System.out.println("both string objects point to the same reference");
System.out.println("== references to the reference");
}
String s3 = new String("hello");
String s4 = new String("hello");
if(s3==s4) {
System.out.println("This will not print, because are not pointing to the same reference");
}
if(s1.equals(s2)) {
System.out.println("\n equals operator checks for the content matches or not");
}
// StringBuffer and StringBuilder are mutable
// StringBuffer is thread safe
// It is synchronized
// If we run the tests in paraller runs
StringBuffer sb = new StringBuffer("hello string buffer"); // StringBuffer is mutable
System.out.println("sb : " +sb);
sb.append(" world");
System.out.println("sb after append: " +sb);
sb.reverse();
System.out.println("sb after reverse: " +sb);
StringBuffer sbMethods = new StringBuffer("hello");
sbMethods.append(" world");
System.out.println("sb after append: " +sbMethods);
sbMethods.insert(2, "she");
System.out.println("sb after insert: " +sbMethods);
sbMethods.replace(5,7, "aa");
System.out.println("sb after replace: " +sbMethods);
sbMethods.deleteCharAt(5);
System.out.println("sb after delete chat: " +sbMethods);
sbMethods.reverse();
System.out.println("sb after reverse: " +sbMethods);
// String Builer is not thread safe
// It is non synchronized
// If we run the tests in squence then it is better , not good in paraller runs
StringBuilder sbuilder = new StringBuilder("hello");
sbuilder.append(" world");
System.out.println("sbuilder after append: " +sbuilder);
}
}
string s1 hello
string s1 after contact: hello
both string objects point to the same reference
== references for the reference
equals operator checks for the content matches or not
sb : hello string buffer
sb after append: hello string buffer world
sb after reverse: dlrow reffub gnirts olleh
sb after append: hello world
sb after insert: heshello world
sb after replace: hesheaao world
sb after delete chat: hesheao world
sb after reverse: dlrow oaehseh
sbuilder after append: hello world
