interface example

/*
can/will someone please provide me with an example of two simple .java files that i can compile and then run that uses an interface?

something like:
*/
public class Tree implements Grows{
Tree oak_A = new Tree;
// stuff suff
}

// thanks to whoever for your time/help...

Barclay Mcdaniel,
Welcome to JavaRanch.

A very simple example can be like:

interface Hello { void sayHello(); } class MyHello implements Hello { public void sayHello() { System.out.println("Hello"); } }


Well, but before you get into this you got to have good understanding what interface and classes are. Can you tell us what you are studying and what you tried?

I am a programmer hobbiest only, can work well with procedural programming- i just get lost in oop, i made this simple math program for my son (below) for simple console 6-year-old-math but want to use oop
in a file named MathWork.java for 'javac' and then runs well as MathWork.class
>>>>>>>>>>>>>>>>>>>>>>>>>>>>

import java.io.*; import java.lang.*; import java.util.*; public class MathWork{ private static BufferedReader stdin=new BufferedReader(new InputStreamReader(System.in)); public static void main(String [] args) throws IOException { char operation; int guess; int answer; int num1; int num2; for(int ct=0;ct<=3;ct++) { do{Random generator = new Random(); num1=generator.nextInt(99); num2=generator.nextInt(20); }while(num2>num1); if(num1%2==2){answer=num1+num2;operation='+';}else{answer=num1-num2;operation='-';} System.out.print("\n"+num1+operation+num2+"="); Scanner input = new Scanner(System.in); try { guess=input.nextInt(); while(guess!=answer){ System.out.print("Incorrect"); System.out.print("\n"+num1+operation+num2+"="); guess=input.nextInt(); }System.out.print("Correct"); }catch(InputMismatchException ime){ System.out.println("no silly, go again..."); }//try-catch }//for ct }//main }//MathWork

what i was wanting with that tree/grows wording was an example that shows simple interface operations, that hello interface example did not help me see it's use/purpose, i read about interfaces lots, examples given in books and the like never show me much...

An object presents a public "interface" to its world. An "interface" adds to that public interface, so it only has methods. [It can have constant fields, but most people think they are a bad idea.]
Examplepublic interface Engine { void start(); void stop(); double useFuel(int distance, int speed); }//end interfaceNow, to create an Engine class, you can "implement" that interface, whihc means that the ;s are replaced by bodies to their methods.
Examplepublic class PetrolEngine implements Engine { private final double litres; public PetrolEngine(double litres) { this.litres = litres; }//end constructor public double getLitres() { return litres; }//end get litres public void start() { System.out.println("Turn key, vroom, vroom."); }//end start public void stop() { System.out.println("Turn key off, thud clunk . . . . "); }//end stop public double useFuel(int speed, int distance) { return speed * speed * distance * Math.sqrt(litres) / 123456.789; }//end use fuel }//end classI have just put any old stuff in the methods, so you can see what is going on.

Notice you now have a class with methods, three of which are "specified" by the three methods in the interface. Notice that although it doesn't say anything about "public" in the interface, the methods are expected to be implemented as "coderanch."
You can also design a DieselEngine class which also implements Engine.

You can give three names to the type of the PetrolEngine: PetrolEngine, Engine and Object. It is implicity all three at the same time.

Don't wish to blind you with science, but I hope that is of some help.

And the beauty of it all is that users of Engines don't need to know anything about the implementation. A using class just addresses the Engine interface and it could care less (and in fact doesn't even know) if the implementation is a PertrolEngine, a DeiselEngine, a SteamEngine, a SquirrelPoweredEngine or a RubeGoldbergConvolutedEngine. Because they all implement Engine, they all act like Engines.

if you looked at the MathWork.java i provided, you'll see i do not know lots about oop, please provide me with a 'simple', not so-many 'engine meathods' as are there, just a simple, maybe 3 java file's code to suport like a tree class that implements a grow interface or something... that i can compile, 'javac', and run 'java' myself...

thanks for someone's time...

barclay

Originally posted by Campbell Ritchie:
. . .public interface Engine . . .. . .
Examplepublic class PetrolEngine implements Engine { private final double litres; public PetrolEngine(double litres) { this.litres = litres; }//end constructor public double getLitres() { return litres; }//end get litres public void start() { System.out.println("Turn key, vroom, vroom."); }//end start public void stop() { System.out.println("Turn key off, thud clunk . . . . "); }//end stop public double useFuel(int speed, int distance) { return speed * speed * distance * Math.sqrt(litres) / 123456.789; }//end use fuel }//end class. . .

public class Car { private Engine engine; private String make; private int speed; //Default value = 0 public Car(String make, Engine engine) { this.make = make; this.engine = engine; }//end constructor public void startEngine() { engine.start(); }//end start engine public void stopEngine() { engine.stop(); }//end stop engine public void speedUp(int mph) { speed += mph; }//end speedUp public void slowDown(int mph) { speed -= mph; }//end slow down public void stop() { speed = 0; }//end stop /** * @return the amount of "fuel" used */ public double drive(int distance) { return engine.useFuel(speed, distance); }//end drive @Override public String toString() { return String.format("A %s with a %s travelling at %dmph", make, engine.getClass().getName(), speed); }//end to string }//end carpublic class CarDemo { /* * I usually avoid putting "real" code in the main method, * but I'll do it this time */ public static void main(String[] args) { Car ford = new Car("Ford", new PetrolEngine(1.3));//1.3 litre engine ford.startEngine(); ford.speedUp(50); System.out.println(ford); System.out.printf("It takes %f fuel to go 50 miles.%n", ford.drive(50)); ford.stop(); ford.stopEngine(); }//end main }//end car demoI am afraid I cannot design a SquirrelPoweredEngine for Bear Bibeault (although one type of electric motor is called squirrel-cage), but you could have an ElectricEnginepublic class ElectricEngine implements Engine { private final double hp; public ElectricEngine(double hp) { this.hp = hp; }//end constructor public double getHP() { return hp; }//end get litres public void start() { System.out.println("Click switch until green light shows."); }//end start public void stop() { System.out.println("Click off, no green light"); }//end stop public double useFuel(int speed, int distance) { return speed * speed * distance * hp / 567.89; }//end use fuel }//end classNow double up the instructions in the CarDemo class so your main method now reads: public static void main(String[] args) { Car ford = new Car("Ford", new PetrolEngine(1.3));//1.3 litre engine Car prius = new Car("Prius", new ElectricEngine(50)); ford.startEngine(); ford.speedUp(50); System.out.println(ford); System.out.printf("It takes %f fuel to go 50 miles.%n", ford.drive(50)); ford.stop(); ford.stopEngine(); prius.startEngine(); prius.speedUp(50); System.out.println(prius); System.out.printf("It takes %f fuel to go 150 miles.%n", prius.drive(150)); prius.stop(); prius.stopEngine(); }//end mainThen see what happens.

And as for treespublic interface GrowingPlant { void grow(); }//end interfacepublic class Tree implements GrowingPlant { private final String species; private int height; public Tree(String species, int startHeight) { this.species = species; height = startHeight; }//end constructor /** * Get 1 foot taller. * Specified by GrowingPlant#grow */ public void grow() { height++; }//end grow @Override public String toString() { return "A " + species + " tree, " + height + " ft tall."; }//end to String }//end tree classpublic class TreeNursery { private Tree[] trees; public TreeNursery() { trees = new Tree[]{new Tree("Beech", 5), new Tree("Sycamore", 3), new Tree("Cherry", 1), new Tree("Leylandii", 5)}; }//end constructor public void go() { /* Print out all the trees */ for (Tree t : trees) { System.out.println(t); }//end for-each for (Tree t : trees) { /* Make each tree 3 foot taller */ for (int i = 0; i < 3; i++) { t.grow(); }//end for }//end for-each /* Print details again */ for (Tree t : trees) { System.out.println(t); }//end for-each /* Make Leylandii shoot up like the pernicious weed it is! */ for (int i = 0; i < 60; i++) { trees[3].grow(); }//end for /* Print details again so we can see which is different */ for (Tree t : trees) { System.out.println(t); }//end for-each }//end go public static void main(String[] args) { new TreeNursery().go(); }//end main }//end tree nursery classNow you can design a Lithops class where the grow method causes it to enlarge by 1mm at a time!

wonderful tree example, just what i was looking for...

thank you

barclay

You're welcome.