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Java Basics 2 A practical tutorial

Package • A class can be placed in a package • This facilitates organizing the classes • Each module can have a number of classes • All these can be placed in one package

Importing classes import com.abc.transport.Car; // need to import classes in other packages public class Travel{ public static void main (String[] args) { Car c = new Car(); c.setType("Audi"); System.out.println("My car is : "+ c.getType()); } } package com.abc.transport; // class Car is placed in package public class Car extends Vehicle { } //Compile : javac –d . *.java

Access specifiers • All private members can be accessed by the same class only • All protected members can be accessed by same, child class and classes in same package • All default members can be accessed by same and classes in same package • All public members can be accessed by all classes in any package

Printing an object • To print an object, • System.out.println(obj); • Will display on console • com.abc.transport.Car@110b053 • In order to print something useful, we have to override toString() method which is defined in Object class • public String toString() { • return “Car is ”+type; • } • Now the output will be • Car is Audi

Comparing two objects • The method • .equals(Object obj) • compares current object with another object • The output is always false as the default implementation in Object class is comparison of references • To change the implementation override the method • public boolean equals(Object obj) { • return this.type == ((Car)obj).getType (); • } • Now the return will be true if type is same in both objects

final variable • public class Employee { • private final String companyName = “ABC Ltd”; • private final String location; • public Employee () { • this.location = “Bangalore”; • } • public Employee (String location) { • this.location = location; • } • } • A final instance variable should be initialized during declaration OR in the constructor. • We can use parameterized constructor to initialize from outside. • new Employee(“Mumbai”);

static field public class StaticTest { public static String str = "Bangalore"; public static void main (String [] args) { StaticTest st1 = new StaticTest(); System.out.println("st1.str :" + st1.str); StaticTest st2 = new StaticTest(); st2.str = "Delhi"; System.out.println("now st1.str :" + st1.str); } } Output is : st1.str :Bangalore now st1.str :Delhi All static fields are shared between objects

String class public class CheckString { public static void main(String[] args) { String str = "This is a city"; StringBuffersbf = new StringBuffer("This is a city"); System.out.println("sbf = "+sbf); CheckStringcs = new CheckString(); cs.updateMe(str); System.out.println("str = "+str); cs.updateMe(sbf); System.out.println("now sbf = "+sbf); } public void updateMe(StringBuffersbf) { sbf.append(" - Bangalore"); } public void updateMe(String str) { str = str.concat( " - Bangalore"); System.out.println("str in updateMe = "+str); }

String class • The output demonstrates that String variable is not modified by the method • This is because String class is immutable • It is a constant • So String is passed by value into the method • If modifications are required, StringBuffer or StringBuilder has to be used

String Pool String s1 = "abc"; String s2 = "abc"; System.out.println("s1= "+s1+", s2= "+s2); System.out.println("s1==s2 : "+(s1==s2)); String s3 = new String("xyz"); String s4 = new String("xyz"); System.out.println("s3==s4 : "+(s3==s4)); • java uses the value from the String pool for s2 as the value is same as s1 • s1==s2 will reveal that both are referring to same object. • This is an example of Java 'FlyweightPattern‘ : object in memory is used if available • new String() will create different object and not from pool

Regular Expressions Sequence of characters that forms a search pattern String ipAddress = "12.34.125.5"; // or args[0] String delimiters = "\\."; String[] tokensVal = ipAddress.split(delimiters); for(String str : tokensVal) System.out.println(str); String idPattern = "^(\\d{3}-?\\d{2}-?\\d{4})$"; String id = "111-22-3333"; // or args[0] Pattern pattern = Pattern.compile(idPattern); Matcher matcher = pattern.matcher(id); System.out.println(matcher.matches()); // id.matches(idPattern); // String supports regex

Password Validation String passwordPattern = "^(?=.*[0-9])(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=])(?=\\S+$).{8,}$“; String pswd= "albertLeo@6"; Pattern pattern = Pattern.compile(passwordPattern); Matcher matcher = pattern.matcher(pswd); System.out.println(matcher.matches());

Email Validation String emailPattern = "^[_A-Za-z0-9-\\+]+(\\.[_A-Za-z0-9-]+)*@[A-Za-z0-9-]+(\\.[A-Za-z0-9]+)*(\\.[A-Za-z]{2,})$";

Best Java training in Bangalore