import java.io.BufferedReader; import java.io.IOException; import java.io.InputStreamReader; import java.util.Scanner; // A simple enum example where enum is declared outside a class // NOTE: enum keyword instead of class keyword enum Day{ SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY; } public class Main { enum Time{ // A simple enum example where enum is declared inside a]class EARLY_MORNING, MID_MORNING, NOON, AFTERNOON, NIGHT; } private static class Parent {} //Superclass private static class Child extends Parent {} //Subclass private static class Vehicle { //Superclass Vehicle int maxSpeed= 120; public void mySpeed(){ System.out.println("Vehicles travel at "+maxSpeed+" km/hr"); } } public static class Cars extends Vehicle { //Subclass Cars int maxSpeed= 180; public void mySpeed(){ System.out.println("Cars travel at "+maxSpeed+" km/hr"); } public void getSpeed() { System.out.println("Maximum speed= "+super.maxSpeed); //print maxSpeed of super class (vehicle) } //Note that display() is only in Cars class public void display() { mySpeed(); //will invoke or call current class mySpeed() method super.mySpeed(); //will invoke or call parent class mySpeed() method } } public static void main(String[] args) throws IOException { readInputMethods(); //automaticTypeConversion(); //explicitTypeConversion(); //whileLoop(); //forLoop(); //doWhileLoop(); //breakKeyword(); //continueKeyword(); //ifStatement(); //nestedIfStatement(); //ifElseStatement(); //ifElseIfStatement(); //switchStatement(); //ternaryOperator(); //nestedTernaryOperator(); //numericLiterals(); //javaEnums(); //instanceOfKeyword(); //superKeywordVariable(); //superKeywordMethod(); //superKeywordConstructor(); } public static void superKeywordConstructor() { } public static void superKeywordMethod() { Cars probox= new Cars(); probox.display(); } public static void superKeyword() { Cars toyota= new Cars(); toyota.getSpeed(); } public static void instanceOfKeyword() { Parent mother= new Parent(); Parent father= new Child(); Child lastBorn= new Child(); if (lastBorn instanceof Child) //Tests if lastBorn is an instanceof Child System.out.println("lastBorn is an instanceof Child"); if (lastBorn instanceof Parent) //Tests if lastBorn is an instanceof Parent System.out.println("lastBorn is an instanceof Parent"); if (lastBorn instanceof Object) //Tests if lastBorn is an instanceof Object System.out.println("lastBorn is an instanceof Object"); if (mother instanceof Parent) //Tests if mother is an instanceof Parent System.out.println("mother is an instanceof Parent"); if (mother instanceof Child) //Tests if mother is an instanceof Child System.out.println("mother is an instanceof Child"); if (father instanceof Parent) //Tests if father is an instanceof Parent System.out.println("father is an instanceof Parent"); if (father instanceof Child) //Tests if father is an instanceof Child System.out.println("father is an instanceof Child"); } public static void javaEnums() { Day getDay= Day.THURSDAY; Time getTime= Time.MID_MORNING; System.out.println(getDay+" "+getTime); } //Numeric literals are used to enhance the readability. public static void numericLiterals() { int inum= 1_000_000; long lnum= 10_000_000; float fnum= 2.100_001F; double dnum= 2.101_121_001; System.out.println("inum: " + inum); System.out.println("lnum: " + lnum); System.out.println("fnum: " + fnum);System.out.println("dnum:" + dnum); } public static void nestedTernaryOperator() { int boyAge= 20; int girlAge= 12; System.out.println( (boyAge<20) ?"Illegal, boy is under 20" :(girlAge<18) ?"Illegal, girl is under 18" :"Marriage acceptable" ); } public static void ternaryOperator() { int age= 12; System.out.println( (age>=18) ?"Can enter, over 18" :"Go away, under 18" ); } public static void switchStatement() { int select= 2; switch (select) { case 1: System.out.println("Selected option 1"); break; case 2: System.out.println("Selected option 2"); break; case 3: System.out.println("Selected option 3"); break; default: throw new AssertionError(); } } public static void ifElseIfStatement() { int age= 18; if (age<=9) System.out.println("Child"); else if (age<=19) System.out.println("Teenager"); else if (age<=30) System.out.println("Youth"); else if (age<=45) System.out.println("Adult"); else if (age<=65) System.out.println("Mature"); else System.out.println("Older"); } public static void ifElseStatement() { int age= 16; if (age<18) System.out.println("You cannot go to clubs"); else System.out.println("You can be a role model"); } public static void nestedIfStatement() { int boyAge= 28; int girlAge= 17; if (boyAge>=20) { if (girlAge>=18) { System.out.println("You can have a wedding"); } } } public static void ifStatement() { int age= 18; if (age<18) System.out.println("You cannot go to clubs"); if (age>=18) System.out.println("You can be a role model"); } public static void continueKeyword() { for (int keepCount= 1; keepCount<=10; keepCount++) { if (keepCount==5) { System.out.println("\tSkipped loop "+keepCount); continue; //causes the loop to skip the remainder of its body and immediately jump to the next iteration of the loop. } System.out.println("Finished loop "+keepCount); } } public static void breakKeyword() { int keepCount= 1; do { if (keepCount==5) break; //terminates the loop System.out.println("Finished loop "+keepCount); keepCount++; } while (keepCount<=10); } public static void doWhileLoop() { int keepCount= 1; do { System.out.println("Finished loop "+keepCount); keepCount++; } while (keepCount<=10); } public static void forLoop() { for (int keepCount= 1; keepCount<=10; keepCount++) System.out.println("Finished loop "+keepCount); //No need for braces since we only have one statement } public static void whileLoop() { int keepCount= 1; while (keepCount<=10) { System.out.println("Finished loop "+keepCount); keepCount++; } } //NOTE: Follows the sequence: double-> float-> long-> int-> short-> byte public static void explicitTypeConversion() { double d= 100.5; int i= (int)d; //explicit type conversion byte b= (byte)i; //explicit type conversion System.out.println("Double value: "+d); System.out.println("Int value: "+i); System.out.println("Byte value: "+b); } //NOTE: Follows the sequence: byte-> short-> int-> long-> float-> double public static void automaticTypeConversion() { byte b= 100; int i= b; //automatic type conversion double d= i; //automatic type conversion System.out.println("Byte value: "+b); System.out.println("Int value: "+i); System.out.println("Double value: "+d); } public static void readInputMethods() throws IOException { Scanner scanInput= new Scanner(System.in); BufferedReader bufferInput= new BufferedReader( new InputStreamReader(System.in)); System.out.println("Input with scanner: "); String fromScan= scanInput.nextLine(); System.out.println("Input with BufferedReader: "); String fromBuffer= bufferInput.readLine(); // NOTE: that System.console() does not work on IDEs as it may require console //String fromConsole= System.console().readLine(); // Using Console to input data from user System.out.println("Scanner: "+fromScan); System.out.println("BufferedReader: "+fromBuffer); //System.out.println("Console: "+fromConsole); } }

Basics