Can I put 2 public classes into one Java code?
For example: I need to turn an inputted word backwards, and then the user can ask to print out an individual character.
I have the first part of the code written, where it changes the word to be backwards, but am not sure how to implement the second part of the code within the first.
import java.util.*;
class backwards_string
{
public static void main(String args[])
{
String original, reverse = "";
Scanner in = new Scanner(System.in);
System.out.println("Please enter a word: ");
original = in.nextLine();
int length = original.length();
for ( int i = length - 1 ; i >= 0 ; i-- )
reverse = reverse + original.charAt(i);
reverse = reverse.toUpperCase();
System.out.println("Your word backwards is: "+reverse);
System.out.println("Choose an individual character to print out: ");
}
}
If the question is: how many top-level (= NOT nested) classes may I have in a single java file?
The answer is: you can have only one top-level class with the public access modifier. Also, in this case the file name has to match the name of the public class within it.
Anyway, peeking at your code:
class backwards_string {
//...
}
The class backward_string is not public, it's default (the access level you obtain when you do not declare any access modifier at all). Therefore you may have as many top-level default classes as you like within the same java file.
If you really want to have more than one public top-level class, then each one has to have its own file source.
Yes, this is possible. You don't have to put it in one file though, you can use different classes. They would have to be in the same package (folder) though.
It would look something like this:
backwards_string.java
import java.util.*;
class backwards_string
{
public static void main(String args[])
{
String original, reverse = "";
Scanner in = new Scanner(System.in);
System.out.println("Please enter a word: ");
original = in.nextLine();
int length = original.length();
for ( int i = length - 1 ; i >= 0 ; i-- )
reverse = reverse + original.charAt(i);
reverse = reverse.toUpperCase();
System.out.println("Your word backwards is: "+reverse);
System.out.println("Choose an individual character to print out: ");
//when you want to use the other class:
DifferentAction_String otherClass = new DifferentAction_String();
otherClass.doThingsWithReverseString(reverse);
}
}
DifferentAction_String.java:
public class DifferentAction_String {
public void doThingsWithReverseString(String reverse) {
//here you do things with the reverse string.
}
}
Related
When I run this program, it does not return anything yet no errors occur. I'm trying to create a method that will return the number of words I previously entered into the array once I enter "".
import java.util.ArrayList;
import java.util.Scanner;
public class ArrayCounter {
public static int CountItems(ArrayList<String> list ) {
int i = list.size();
return i;
}
public static void main (String args[]) {
ArrayList<String> Names = new ArrayList<String>();
Scanner input = new Scanner(System.in);
while(true) {
System.out.println("Hey gimme a word");
String word = input.nextLine();
if (word.equals("")) {
System.out.println("The number of values entered were:");
break;
} else {
Names.add(word);
}
}
CountItems(Names);
input.close();
}
}
You're ignoring the result returned from CountItems.
The println should be:
System.out.println("The number of values entered were: " + CountItems(Names));
As an aside, methods names in Java should start with a lowercase, so CountItems should instead be countItems.
Your CountItems method returns the item count, but you are ignoring the result. You need some kind of System.out.println(CountItems(Names)) to print the result to the console.
Also, please consider renaming CountItems to countItems and Names to names to follow the naming conventions for Java.
package BankingSystem;
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;
public class Bank {
public static void main(String [] args){
List<String> AccountList = new ArrayList<String>();
AccountList.add("45678690");
Scanner AccountInput = new Scanner(System.in);
System.out.println("Hi whats your pin code?");
AccountInput.nextLine();
for (int counter = 0; counter < AccountList.size(); counter++){
if (AccountInput.equals(AccountList.get(counter))){ //If Input = ArrayList number then display "hi"
System.out.println("Hi");
}
else { //If not = to ArrayList then display "Incorrect"
System.out.println("Incorrect");
}
}
}
}
Hi, in here I am trying to match the userInput to arrayList, if its correct then display "hi" if not display "Incorrect", for the incorrect part do I to use exception handling? and how can I get it to match the ArrayList number - 45678690?
.nextLine() returns a string which needs to be assigned to a variable ....
And then compare the variable with elements in the arraylist using .contains() method ...
If you also want the index position use .indexOf() method ...
String input = AccountInput.nextLine();
if(AccountList.contains(input))
// do something
else
// do something else
First things first you need to store your user's input into some string as you currently aren't doing that.
Instead of using a counter and iterating through your list you can instead just use
AccountList.contains(the string variable assigned to AccountInput)
If it's false then the entry isn't there, otherwise it's in there. The exception handling you might want to use in this scenario would be to handle a user inputting letters instead of numbers.
You have to store the input value in a string to check the number :
String value = AccountInput.nextLine();
if (value.equals(AccountList.get(counter))) ...
Start variables with lower case. Names that start with upper case is for Classes only in java. So use List<String> accountList , and not List<String> AccountList .
The main problem in your code is that you are comparing the elements in list with the Scanner-object. And that will always be false.
You also never store the input from the Scanner any place.
You need to place the return value somewhere, like
String input = scanner.nextLine();
and compare the strings in the list to this string, not the Scanner-object.
I've added a flag so that it works correctly with multiple items in the accountList.
List<String> accountList = new ArrayList<String>();
accountList.add("45678690");
accountList.add("1");
accountList.add("0");
Scanner scanner = new Scanner(System.in);
System.out.println("Hi whats your pin code?");
String accountInput = scanner.nextLine();
boolean listContainsInput = false;
for (int counter = 0; counter < accountList.size(); counter++){
if (accountInput.equals(accountList.get(counter))){
listContainsInput = true;
break;
}
}
if(listContainsInput) {
System.out.println("Hi");
} else {
System.out.println("Incorrect");
}
You are comparing the instance of the Class Scanner
Scanner AccountInput = new Scanner(System.in);
To a String:
AccountInput.equals(AccountList.get(counter))
(ArrayList.get(int) returns a String or fires an Exception)
You need to start with comparing String to String first:
AccountInput.nextLine().equals(AccountList.get(counter))
If you need additional debbuging see how both strings look like(e.q. print 'em)
Here is documentation on Scanner:
https://docs.oracle.com/javase/7/docs/api/java/util/Scanner.html
Read it, scanner is important thing in programming languages.
First of all, thanks for reading!
I made a class "Sportsman" that is the Superclass of "Footballer".
So I made an array of Sportsman-objects that also contains Footballer objects, no problems here (I have a pretty good idea of how inheritance works).
I can set Footballer-specific variables to the objects in the array, but when I want to print the variables I've just declared to the object i can't call get-methods because the array is a Sportsman-array and not a Footballer-array.
So here is my question: How do i print the Footballer specific variables from a Sportsman Superclass array?
Things to know:
I can't make a separate array for the subclass objects. They must be mixed!
While putting a subclass object in the arrays of superclass objects, I explicitly make it a subclass object. However, I'm not able to use subclass methods on it.
main code:
public class SportApp {
public static void main(String[] args)
{
Scanner input = new Scanner(System.in);
Sportsman[] sportArr = new Sportsman[10];
for(int count=0 ; count < sportArr.length ; count++)
{ System.out.println("Is the sportsman a footballer?");
String answer = input.nextLine();
System.out.println("Last name?");
String lastName = input.nextLine();
System.out.println("name?");
String name = input.nextLine();
switch (answer){
case "yes": System.out.println("Which club does he play in?");
String club = input.nextLine();
System.out.println("At what position?");
String pos = invoer.nextLine();
sportArr[count]=new Footballer(lastName,name,club,pos);
break;
default: System.out.println("What sport?");
String sport = input.nextLine();
sportArr[count]=new Sportsman(lastName,name,sport);
}
}
System.out.println("All sportsmen that don't play football:");
for(int count=0 ; count < sportArr.length ; count++)
{ if(!(sportArr[count] instanceof Footballer))
{ System.out.print("name: ");
sportArr[count].print();} }
System.out.println("All football players sorted by position:");
//Same as previous print, but with added player position and club!
for(int count=0 ; count < sportArr.length ; count++)
{ if(sportArr[count] instanceof Footballer)
{
/*what I've tried:
*System.out.println("front players:");
*if(sportArr[count].getPos()=="front") //the .getPos doesn't work because it wants to invoke it on a Sportsman where getPos doesn't exist
*{ sportArr[count].print();} //as the problem above, it doesn't see the object is also a Footballer so it does the Sportsman print()
*
*I wanted to do a regular sportArr[count].pos to print the Position but even now it doesn't recognise the object as Footballer, so I can't see pos.
*/
}
}}}
You've done a type check with instanceof in the loop, and if it succeeds, you know that you have a Footballer. So, now you have to cast the object to get the correct type:
if(sportArr[count] instanceof Footballer)
{
Footballer fb = (Footballer) sportArr[count];
// Now this should work (note the use of fb, and not using `==` with string literals):
if(fb.getPos().equals("front")) {
// etc..
}
}
I am trying to figure out how to accumulate user inputs in for loop and then to print them out with one system.out.print. This is my test code for the problem.
So for example if a user type : Mike for his name and Joe,Jack,Dave for other names, how to print them all just having one variable because amount of variables are not known since a user has that decision. Also is it possible to do that without stringbuilder and without arrays?
import java.util.Scanner;
public class Accumulate {
public static void main(String[] args) {
String othernames = " ",name;
int count,n;
Scanner kybrd = new Scanner(System.in);
System.out.println("Enter your name ");
name = kybrd.nextLine();
System.out.println("How many other names would you like to add ? ");
count = kybrd.nextInt();
kybrd.nextLine();
for(n=0;n<count;++n){
System.out.println("Enter other names ");
othernames = kybrd.nextLine();
}
System.out.println("Other names are "+othernames + " And your name is "+ name);
}
}
You can call it recursively, for instance:
Scanner sc = new Scanner(System.in);
String s;
while(condition) {
s = s + sc.nextLine();
}
this will always concat the lines you enter, you can also add commas, or spaces, or whatever you want to add.
as for your question about using Objects other than StringBuilder you can use List<String> and build a string for it at the final step.
you can use Map<String, String> if you need more complex data structure.
I have got one string array each in 2 different classes in java.
When I enter a value from any of the arrays, I want to get the class to which that array value belongs.
So how do I get to know the class just by entering an array value?
eg:
import java.io.*;
class Car {
public static void main(String args[]) throws Exception {
System.out.println("The parts of a car are as follows");
for (int i = 1; i <= 5; i++) {
System.out.println(i + str[i]);
}
for (int j = 1; j <= 5; j++) {
System.out.println(j + ch[j]);
}
DataInputStream dis = new DataInputStream(System.in);
System.out.println("Choose and enter any part name to group it under following categories:" + "\n" + "Engine" + "\t" + "\t" + "Bonet");
String part = dis.readLine();
if (part == ch[]) {
System.out.println("Your choosen part is " + part + " and it comes under Engine category");
} else {
System.out.println("Your choosen part is " + part + " and it comes under Bonet category");
}
}
}
class Engine {
String ch[] = {"asd", "fgh"};
}
class Bonet {
String str[] = {"qwe", "rty"};
}
now when a user enters asd i want to display to which class it belongs
I wont give you full code because I believe that creating it yourself will be better for you. Instead here are few facts that you need to take into consideration:
To have access to array stored in other class you would aether have to create instance of that class
Engine engine = new Engine();
engine.ch[0];
or in your case you should probably make your array static
class Engine {
static String ch[] = { "asd", "fgh" };
}
and access it via class name Engine.ch[0]
Arrays are indexed from 0 to arraySize-1
To get size of array you can use its filed length and later use it like
for(int i=0; i<Bonet.str.length; i++){
System.out.println(i+Bonet.str[i]);
}
readLine() from DataInputStream is depracated. Instead you can use nextLine from java.util.Scanner
Scanner scanner = new Scanner(System.in);
//...
String part = scanner.nextLine();
To check if some object is stored in array you will have to iterate over all elements of that array and compare them with your object. Also remember that to compare String objects you should use equals method like part.equals(otherString).
But to make it with less code you can wrap your array into List and use its contains(Object o) method. To wrap array into list you can use asList method from java.util.Arrays class.
if(Arrays.asList(Engine.ch).contains(part)){...
Bare minimum changes to get this to work are as below. Key points:
the contents of Engine and bonet belong to instances of those classes not to car
arrays of size 5 have indicies 0,1,2,3,4, not 1,2,3,4,5
Where going through an array in a loop do not hard code the array size, use .length instead
import java.io.*;
public class Car {
public static void main(String args[]) throws Exception {
System.out.println("The parts of a car are as follows");
Engine engine=new Engine(); //we must create any components we have
Bonet bonet=new Bonet(); //we must create any components we have
for (int i = 0; i <bonet.str.length; i++) {
System.out.println(i +":"+ bonet.str[i]);
}
for (int j = 0; j < engine.ch.length; j++) {
System.out.println(j +":"+ engine.ch[j]);
}
DataInputStream dis = new DataInputStream(System.in);
System.out.println("Choose and enter any part name to group it under following categories:" + "\n" + "Engine" + "\t" + "\t" + "Bonet");
String part = dis.readLine();
boolean isInEngine=false; //assume isn't in engine, try to prove otherwise
for(int i=0;i<engine.ch.length;i++){
if (engine.ch[i].equals(part)){
isInEngine=true;
}
}
if (isInEngine==true) {
System.out.println("Your choosen part is " + part + " and it comes under Engine category");
} else {
System.out.println("Your choosen part is " + part + " and it comes under Bonet category");
}
}
}
class Engine {
String ch[] = {"asd", "fgh"};
}
class Bonet {
String str[] = {"qwe", "rty"};
}
Note; this is far from an optimal solution, ideas to consider:
It is bad practice to refer to the insides of annother class like this, it would be better for each class (engine and bonnet) to include a method .testPart(String string) that would return a boolean as to if it contains the part
The code assumes that if its not in engine it must be in bonet, what if the user enters something crazy
An array list (rather than an array) would allow us to use .contains(String string) rather than using a loop to look though the array
The DataInputStream is no longer supported (note that it appears with a strike through in most IDEs), consider using Scanner scanner = new Scanner(System.in); and then use scanner.nextLine(); to get the line
What if you add a third type of component, better to hold all your parts in an array, then you can easily add annother. An interface (or abstract base class) would promise that all the array contents held the .testPart(String string) and a getName() method; the array/arraylist would be declared as containing the interface/abstract-base-class
You never actually create an instance of Car, which you would do by Car car=new Car();, the Car class could then have methods like car.printOptions(); and car.testComponent(String testString);. The way you're doing it (one long main function) will work fine for small programs, but the bigger your program becomes the harder it will be to work like this. In this case the engine and bonet would be fields of the car class (which logically makes a lot more sense than them just 'hanging around')