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Calling a boolean method from a class

i just made a problem which should return if a number "isHappy" or not. A number is happy if it meets some criteria:
A happy number is a number defined by the following process:
-Starting with any positive integer, replace the number by the sum of the squares of its digits.
-Repeat the process until the number equals 1 (where it will stay), or it loops endlessly in a cycle which does not include 1.
-Those numbers for which this process ends in 1 are happy.
`
import java.util.HashSet;
import java.util.Set;
class Solution{
public int getNext(int n){
int totalSum = 0;
while(n > 0){
int last = n % 10;
n = n / 10;
totalSum += last * last;
}
return totalSum;
}
public boolean isHappy(int n){
Set<Integer> seen = new HashSet<>();
while( n!=1 && !seen.contains(n)){
seen.add(n);
n = getNext(n);
}
return n==1;
}
}
class Main {
public static void main(String[] args){
isHappy(23); //this doesnt work.
}
}
`
I don't know how to call this function, tried different methods like int number = 23 for ex and then isHappy(number) sout(isHappy(number)); , number.isHappy() although this makes no sense, intellij is telling me to make a method inside main but i dont think i must do this, think there s another way.

There are a couple of problems here. When you run a Java application it looks for the main method in the class you run. Your class has no main method, instead it has an inner class that has a main method.
class Solution {
// existing methods
// no 'Main' class wrapping method
public static void main(String[] argv) {
}
}
The second problem is that main is a 'static' method but isHappy is an 'instance' method. To call it you need an instance of the class
// inside the `main` function
var sol = new Solution();
if (sol.isHappy(23)) {
System.out.println("23 is happy");
} else {
System.out.println("23 is not happy");
}

You have completely solved the problem. You only have to decide what to do with the result of your calculations. You can simply print a string depending on the result.
Please note, that the methods in your Solution class are not static. So, you need to create an instance of the class and call the methods on that instance.
import java.util.HashSet;
import java.util.Set;
class Solution {
public int sumOfDigitsSquares(int n) {
int totalSum = 0;
while (n > 0) {
int last = n % 10;
n = n / 10;
totalSum += last * last;
}
return totalSum;
}
public boolean isHappy(int n) {
Set<Integer> seen = new HashSet<>();
while (n != 1 && !seen.contains(n)) {
seen.add(n);
n = sumOfDigitsSquares(n);
}
return n == 1;
}
}
class Main {
public static void main(String[] args) {
var solution = new Solution();
String answer = solution.isHappy(23) ? "Is happy" : "Not happy at all";
System.out.println(answer);
}
}
Here is one possible way to check all numbers from 1 to 100 for happiness and print the result for each number.
IntStream.rangeClosed(1, 100)
.mapToObj(i -> "" + i + " " + (solution.isHappy(i) ? "is happy" : "not happy"))
.forEach(System.out::println);

To call non-static methods of a class, you need an instance:
public static void main (String [] args) {
Solution foo = new Solution ();
boolean bar = foo.isHappy (49);
// do something with bar
}
To use a static method, you don't use an instance:
class Solution{
public static int getNext(int n){ ... etc ...
}
public static boolean isHappy(int n){ ... etc ...
}
public static void main (String [] args) {
boolean foo = isHappy (1024);
// do something with foo
}
Another problem is you are throwing away the result of isHappy (23).
System.out.println (isHappy(23));
System.out.println ("is 23 happy?" + (isHappy(23) ? "Yes" : "No");
are two possibilities.

need assistance with a input issue in java [duplicate]

This question already has answers here:
Error in System.out.println
(5 answers)
Closed 4 years ago.
My Task:
Create a class called Icosahedron which will be used to represent a regular icosahedron, that is a convex polyhedron with 20 equilateral triangles as faces. The class should have the following features:
A private instance variable, edge, of type double, that holds the
edge
length.
A private static variable, count, of type int, that holds the
number of Icosahedron objects that have been created.
A constructor that takes one double argument which specifies the edge length.
An
instance method surface() which returns the surface area of the
icosahedron. This can be calculated using the formula 5*√3 edge².
An
instance method volume() which returns the volume of the icosahedron.
This can be calculated using the formula 5*(3+√5)/12*edge³.
An
instance method toString() which returns a string with the edge
length, surface area and volume as in the example below:
Icosahedron[edge= 3.000, surface= 77.942, volume= 58.906]
The numbers in this string should be in floating point format with a field
that is (at least) 7 characters wide and showing 3 decimal places.
Please use the static method String.format with a suitable formatting
string to achieve this. A static method getCount() which returns the
value of the static variable count.
Finally, add the following main method to your Icosahedron class so that it can be run and tested:
public static void main(String[] args) {
System.out.println("Number of Icosahedron objects created: " + getCount());
Icosahedron[] icos = new Icosahedron[4];
for (int i = 0; i < icos.length; i++)
icos[i] = new Icosahedron(i+1);
for (int i = 0; i < icos.length; i++)
System.out.println(icos[i]);
System.out.println("Number of Icosahedron objects created: " + getCount());
}
Okay. so heres what i have started on:
import java.util.Scanner;
public class Icosahedron {
private double edge = 0;
private int count = 0;
Scanner input = new Scanner(System.in);
double useredge = input.nextDouble();
System.out.println("Enter Edge Length: ");
}
i receive an error on the last line. i cant use println() what am i doing wrong? or maybe im understanding the question wrong? any guidance would be appreciated.
thanks.

Your Icosahedron class should look like the following:
public class Icosahedron {
private double edge;
private int count;
public Icosahedron(int count) {
this.count = count;
}
public double getEdge() {
return edge;
}
public void setEdge(double edge) {
this.edge = edge;
}
public int getCount() {
return count;
}
public void setCount(int count) {
this.count = count;
}
#Override
public String toString() {
return "Icosahedron{edge=" + edge + ", count=" + count + '}';
}
}
And your class containing the main method (I called it MoreProblem):
import java.util.Scanner;
public class MoreProblem {
public static void main(String[] args) {
Icosahedron[] icos = new Icosahedron[4];
for (int i = 0; i < icos.length; i++) {
icos[i] = new Icosahedron(i+1);
Scanner input = new Scanner(System.in);
System.out.println("Enter Edge Length: ");
double userEdge = input.nextDouble();
icos[i].setEdge(userEdge);
}
for (Icosahedron icosahedron : icos) {
System.out.println(icosahedron);
}
System.out.println("Number of Icosahedron objects created: " + icos.length);
}
}

Create method that prints the numbers between two specified numbers

So I'm creating a method in that is supposed to print the numbers between two specified numbers. I had it setup before in the main method but i can figure out how to make a method and call it into the main method. What my program does right now is it only prints what "int between" is equal to. I don't want anyone to just type the code out for me, i'm just looking for tips on what i should change. Last time i asked a question someone proceeded to just answer with code and it did not help me to learn anything.
So my question is what is causing the program to only display what between is equal to? I know that I need a value for the if loop to return something, but it needs to return the numbers between num1 & num2. My Professor Also said that the method needs to be "public static void Printer(int num1, int num2)" is that even possible? I kept getting an error so I switched to "int Printer".
package nortonaw_Assignment8;
public class Nortonaw_Assignment8 {
public static void main(String[] args) {
int between;
between = Printer(5, 20);
System.out.println(between);
}
public static int Printer (int num1, int num2){
int between = 0;
for (;num1<=num2; num1++);
return between;
}
}

1) There's a difference between printing out a value and returning a value.
When you"print" a value in a function, you are just writing out the value to screen or some other medium , but when you use the return statement, you are passing what you are returning to the caller of your function as well as control.
** I hope that makes sense to you?
2)"public static void Printer(int num1, int num2)" is possible.

currently your method is designed to return only one single number, so either you return a collection of numbers are you print the numbers inside Printer, in this case you can use the method signature suggested by your professor.
So I would write it like this:
public static void main(String[] args) {
Printer(5, 20);
}
public static void Printer (int num1, int num2) {
for (int i=num1;i<=num2; i++) {
System.out.println(i);
}
}
EDIT:
Note that I introduced a additional counter variable i because I think num1 and num2 should not be changed as they define the boundary of your range.

package printingTasks;
public class Printer {
public static void main(String[] args) {
printInBetween(25, 30); //Would print 26 -> 29
}
/*
* You don't need to return something if you just want to print it out to the console.
* So you can use void as return type
*/
public static void printInBetween(final int leftBoundary, final int rightBoundary){
/**
* Calculate the first number which should be printed.
* This number would be the leftBoundery plus one
* This number will be the starting point of your loop
*/
final int firstNumber = leftBoundary + 1;
// final int firstNumber = leftBoundary; //if you want to include the left boundary
for (
int currentNumber = firstNumber; //Set the counter of the the loop (currentNumber) to the first valid number
currentNumber < rightBoundary; //Run the loop while the loop counter is less than the rightBoundary
// currentNumber <= rightBoundary; //If you want to include the right boundary
currentNumber++ //Increment the loop counter with each iteration
){
/**
* In each iteration you will print the current value of the counter to the console
* Because your counter (currentNumber) will be incremented from the first valid number
* to the last number before the right boundary you will get all numbers between the two
* boundaries.
*/
System.out.println(currentNumber);
}
}
}

Your teacher wants you to print from the Printer method not directly in the main method. All the main method should be doing is calling the Printer method.
Here is the full snippit:
package nortonaw_Assignment8;
public class Nortonaw_Assignment8 {
public static void main(String[] args) {
Printer(5, 20);
}
public static void Printer (int num1, int num2) {
for (int i = num1+1;i<=num2-1; i++) {
System.out.println(i);
}
}
}

Is it possible to link integers from a method to a class?

I have a quick question out of curiosity...if I declare an integer in one method, for example: i = 1, is it possible for me to take that i and use its value in my main class (or another method)? The following code may be helpful in understanding what I'm asking...of course, the code might not be correct depending on what the answer is.
public class main {
public main() {
int n = 1;
System.out.print(n + i);
}
public number(){
i = 1;
}
}

No you cannot! Not unless you make it an instance variable!
Or actually send it to the function as an argument!

First, let's start simple. All methods that are not constructors require a return type. In other words,
public void number(){
i = 1;
}
would be more proper.
Second: the main method traditionally has a signature of public static void main(String[] args).
Now, on to your question at hand. Let's consider a few cases. I will be breaking a few common coding conventions to get my point across.
Case 1
public void number(){
i = 1;
}
As your code stands now, you will have a compile-time error because i is not ever declared. You could solve this by declaring this somewhere in the class. To access this variable, you will need an object of type Main, which would make your class look like this:
public class Main {
int i;
public static void main(String[] args) {
Main myMain = new Main();
myMain.number();
System.out.print(myMain.i);
}
public void number(){
i = 1;
}
}
Case 2
Let's say you don't want to make i a class variable. You just want it to be a value returned by the function. Your code would then look like this:
public class Main {
public static void main(String[] args) {
Main myMain = new Main();
System.out.print(myMain.number());
}
public int number(){ //the int here means we are returning an int
i = 1;
return i;
}
}
Case 3
Both of the previous cases will print out 1 as their output. But let's try something different.
public class Main {
int i = 0;
public static void main(String[] args) {
Main myMain = new Main();
myMain.number();
System.out.print(myMain.i);
}
public void number(){
int i = 1;
}
}
What do you think the output would be in this case? It's not 1! In this case, our output is 0. Why?
The statement int i = 1; in number(), it creates a new variable, also referred to as i, in the scope of number(). As soon as number() finishes, that variable is wiped out. The original i, declared right under public class Main has not changed. Thus, when we print out myMain.i, its value is 0.
Case 4
One more case, just for fun:
public class Main {
int i = 0;
public static void main(String[] args) {
Main myMain = new Main();
System.out.print(myMain.number());
System.out.print(myMain.i);
}
public int number(){
int i = 1;
return i;
}
}
What will the output of this be? It's 10. Why you ask? Because the i returned by number() is the i in the scope of number() and has a value of 1. myMain's i, however, remains unchanged as in Case 3.

You may use a class-scope field to store you variable in a class object or you can return it from one method or pass it as a parameter to the other. Mind that you will need to call your methods in the right order, which is not the best design possible.
public class main {
int n;
int i;
public main() {
n = 1;
System.out.print(n + i);
}
public number(){
i = 1;
}
}

Yes, create a classmember:
public class Main
{
private int i;
public main() {
int n = 1;
System.out.print(n + i);
number();
System.out.print(n + i);
}
public number(){
i = 1;
}
}

void method(){
int i = 0; //has only method scope and cannot be used outside it
}
void method1(){
i = 1; //cannot do this
}
This is because the scope of i is limited to the method it is declared in.

Setting values to parameters in a constructor in Java

I just wanted to ask basically what the title says. Here's my example and I want x to be the new set random. I also am doing this off a phone switch doesn't support an equal sign so - means equal. Also the bracket is (. So when I do
Constructor a - new Constructor(x)
public class Opponent (
public static x - 0;
public Opponent (int value) (
value - 5;
)
public static void main (String() args) (
Opponent character1 - new Opponent(x)
System.out.println(x);
)
)
Basically I want x to become 5. The game I am developing concerns randomization then the values should give them to the parameter to the newly created character.
Problem I am having is that its not working which means it probably can't do this.
Is there anyway I can do this.
I apologize if it is a dumb question though but anyways thanks.

public class Opponent {
public static int x = 0;
public Opponent (int value) {
x = value;
}
public static void main (String[] args) {
int y = 5; // random number I chose to be 5
Opponent character1 = new Opponent(y);
System.out.println(character1.x + ""); // will display 5 (which was int y)
}
}
List of Problems:
• To open/close a method/class, don't use ( and ); you have to use { and }
• public static void main (String() args) needs to be public static void main (String[] args)
• To initialize something, use =, not -.
• You need to give x a type, such as int.
• When you defined Opponent character1 - new Opponent(x), you need to have a semi-colon at the end.
• You passed x as a parameter in the line Opponent character1 = new Opponent(y);, even though you were trying to define x with the parameter. Give it a different value.
One note: why would you define an instance of the class in the class? Instead of using this:
Opponent character1 = new Opponent(y);
System.out.println(character1.x + "");
You could just write this:
System.out.println(Opponent.x + "");
However, you could create character1 if you were accessing class Opponent from a different class.

I honestly don't know what your question is, but try running this:
public class Opponent {
public int x;
public Opponent (int value) {
x = value;
}
public static void main (String[] args) {
Opponent character1 = new Opponent(5);
System.out.println(character1.x); // this will output: 5
}
}
A few problems with your question:
you are trying to initialize a static variable thinking its an instance variable?
x is not initialized in main()
value is not defined as a field in Opponent

maybe something like this. i leave the random number generation up to you:
public class Opponent
{
private int score;
public Opponent()
{
// you probbaly want to override this with
// a random number generator
this.score = 0;
}
public Opponent(int value)
{
this.score = value;
}
public int getScore()
{
return this.score;
}
public void setScore(int score)
{
this.score = score;
}
public static void main(String[] args)
{
Opponent character1 = new Opponent();
Opponent character2 = new Opponent(5);
int result = character1.getScore() - character2.getScore();
System.out.println(result);
}
}