Ask user for 3 integers and find out if they make a triangle or not.

[Campbell Ritchie]

I think a few more hints are in order. By the way: once you have got these methods working for ints, you will find it easy to create methods for entry of doubles, BigIntegers, BigDecimals, etc. They will look almost the same as getInt.

/**
 * Get an <code>int</code> from the keyboard. Prints the request message,
 * then the user enters the input. If not valid <code>int</code> prints error message,
 * and if value outwith requested range prints different error message.
 * ... 
 *@param message A message to request the input
 *@param min The smallest input permissible. Must not be larger than max.
 *@param max The largest input permissible. Must not be smaller than min.
 *@something if max is less than min
 */
public static int getInt(String message, int min, int max)
{
   if (max < min)
   {
      // do something
   }
   int i = getInt(message);
   // do something different
   return i;
}

The documentation comment is an essential part of the method because you will be using that class again and again. There is a part of the description missing in line 5. There is a corner case where min == max which I have not specifically addressed. I shall leave it to you whether you permit that corner case or not.

[Ganesh Patekar]

Yes I've used documentation comment in my project. I can make method for double( rather than float), BigIntegers, BigDecimals whichever I want. Thank you for help, you solved my big issue which was pending since ages.  
Last question suppose I want store age of a person and age value definitely be within 0 to 100(Just assume). As we know range of byte is -128 to 127 which fits in our requirement i.e. 0 to 100 then Is It good to declare age as byte rather than int? where int takes more size in memory compared to byte?

[Campbell Ritchie]

If you try to do anything with it, your byte will be promoted to an int anyway, so why worry about 24 bits of memory?

[Ganesh Patekar]

Oh yes that's true.

[Paweł Baczyński]

Not to mention that it would be burdensome to use.
Consider this example:

class Person {
    byte age;

    public Person(byte age) {
        this.age = age;
    }
}

public class Temp {
    public static void main(String[] args) {
        new Person(34); // doesn't compile
        new Person((byte) 34); // you need to cast!!!
    }
}

[Ganesh Patekar]

Paweł Baczyński wrote:

new Person(34); // doesn't compile
new Person((byte) 34); // you need to cast!!! 

hahaha yes I realised that by default It's int,using byte for that means putting myself in trouble. Sometimes I think about weird things

[Campbell Ritchie]

Nothing weird about it; you s‍hould find out about that sort of thing here where it doesn't matter if you are corrected.

[Ganesh Patekar]

Yes I'm always ready

[Bod MacNeil]

I'm guessing I should be throwing an Exception here instead of just System.out.println()?   ANything else I could make better?  Would it be worth putting in a try, catch?  

 int[] nums = new int[3];
    int counter = 0;
    int counter2 = 1;
    int intHolder = 0;
  
    
    
    Scanner sc = new Scanner(System.in);
   
    
   while(counter < 3){
       System.out.println("Enter number: " + counter2);
    
       if(sc.hasNextInt()){
           nums[counter] = sc.nextInt();
           counter++;
           counter2++;
       }
       else {
           System.out.println("Error!");
           sc.next();
          
       }
     
   }

[Knute Snortum]

An exception should be reserved for things that are truly exceptional.  Here, it is expected that the user might enter an ill-formed number.  Your current code is the correct approach.

[Ganesh Patekar]

You can remove int counter2 and print number information like

System.out.println("Enter number: " + ( counter + 1 ) );// It'll not increment counter

Where are you using  int intHolder?

[Bod MacNeil]

Fixed. Thanks

IntHolder was a variable in my last faild attempt which I forgot to delete

[Ganesh Patekar]

You're welcome

[Bod MacNeil]

Hey guys.  I've been trying to add an input Utility class for user input.  What i do is call the method in the utility class 3 times.  If I wanted to do this in a while loop, would I need to use an array instead of variable - sideA, sideB and sideC?   When user enters invalid input, it just goes to the next variable instead of staying on the same one.  

// Method inside Triangle class which calls triangleInput method inside InputUtility class

public void getUserInput(){
         int counter = 0;
         
        System.out.println("Enter 3 integer numbers\n"
                + "which represent 3 sides of a triangle\n"
                + "Press enter after each number\n\n");
         
        //calls ImportUtillity class for user input
        sideA = triangleInput();
        sideB = triangleInput();
        sideC = triangleInput();
        
        validateTri();
    }

// This is the whole Triangle class

import java.util.*;
import static myfirst.ImportUtility.triangleInput;


public class Triangle {
   private int sideA = 0;
   private int sideB = 0;
   private int sideC = 0;
    Scanner UserInput = new Scanner(System.in);
    
    public void getUserInput(){
         int counter = 0;
         
        System.out.println("Enter 3 integer numbers\n"
                + "which represent 3 sides of a triangle\n"
                + "Press enter after each number\n\n");
         
        //calls ImportUtility class for user input
        sideA = triangleInput();
        sideB = triangleInput();
        sideC = triangleInput();
        
        validateTri();
    }
    
    //work out if the 3 side make up a valid triangle
    private void validateTri(){
        
    
        if(sideA + sideB > sideC && sideA + sideC > sideB && sideB + sideC > sideA){
            System.out.print("True");
           PyTheory();
            }
        else {
            System.out.println("False");
            
        }
    }
    
    //work out of the triangle is a right triangle
    private void PyTheory(){
     
        
        //prints true if the square root of sideB and sideC are equal to sideA
        if(sideA > sideB && sideA > sideC){
            
            if(((sideB * sideB) + (sideC * sideC)) == (sideA * sideA)){
                System.out.println("/true");
            }
                else {
                        System.out.println("/false");
                        }
            }
        
        //prints true if the square root of sideC and sideA are equal to sideB
        else if(sideB > sideC && sideB > sideA){
               
        
            if(((sideA * sideA) + (sideC * sideC)) == (sideB * sideB)){
                System.out.println("/true");
            }
                else {
                        System.out.println("/False");
                        }
            }
        
        //prints true if the square root of sideB and sideA are equal to sideC
        else if(sideC > sideB && sideC > sideA){
           
            //System.out.println(Math.sqrt(sideB) - (Math.sqrt(sideA) + Math.sqrt(sideC)));
            if(((sideA * sideA) + (sideB * sideB)) == (sideC * sideC)){
                
                System.out.println("/true");
            }
          
        else{
            System.out.println("/false");
        }
        }
      
    }
}

//This is the whole importUtility class

import java.util.Scanner;

public class ImportUtility {
    private static int intSides = 0; //to hold the user input for returning
    private static int counter = 1;
   
    static Scanner sc = new Scanner(System.in);
    
    private ImportUtility(){
        throw new UnsupportedOperationException("do not create an object of this class"); 
    }
    
    public static int triangleInput(){
        System.out.println("Numer " + counter);
        
        if(sc.hasNextInt()){
            intSides = sc.nextInt();
            counter++;
           
           
        }
        else {
            System.out.println("Error, try again!");
            sc.next();
        }
       return intSides;
    }


}

[Knute Snortum]

This is the code that needs a loop when you don't get good input:

    public static int triangleInput(){
        System.out.println("Numer " + counter);
         
        if(sc.hasNextInt()){
            intSides = sc.nextInt();
            counter++;
        }
        else {
            System.out.println("Error, try again!");
            sc.next();
        }
       return intSides;
    }

Also, you should declare intSides inside this method.

[Ganesh Patekar]

As Knute mentioned, you can use while loop in triangleInput() method.
What is our condition? Ask user to input value until user enters a valid input value. So loop block will have code for asking input from user. But how long to execute loop ? what is the condition of valid input value?. The condition for valid input is input should be an int (If you want floating-point numbers then use double) value so execute while loop until hasNextInt returns true means execute while loop until user enters int value. Just convert these textual statements into code.

[Ivan Jozsef Balazs]

Fred Kleinschmidt wrote:

isTriangle =  ((a+b)>c) || ((a+c)>b) || ((b+c)>a);

Not "or" but "and" operators are needed here.

[Fred Kleinschmidt]

That's right. Typed too fast.

[Ivan Jozsef Balazs]

If a,b,c are positive then at most one of these guys can be non-positive:
-a+b+c
+a-b+c
+a+b-c

Namely the greatest among them against the sum of the others. Because if we take not the greatest, it can not balance against the one proving its being not the greatest, let alone the sum of the two others. Another reasoning: the sum of two of the guys there is 2a, 2b and 2c respectively. So if two among them were non-positive, so would be their sum, the double of a given quantity.

So all three numbers above are positive if and only if their product is positive.

This equivalence might be mathematically correct but computationally not forcibly the ideal criterium.

[Bod MacNeil]

I thought my while loop would run at least once as sc.hasNextInt() should return false as nothing is passed to it?  Would a do while loop be better?  I tried that also and it didn't work.

public static int triangleInput(){
        int intSides = 0; //to hold the user input for returning
        
        
       while(!sc.hasNextInt()){
           System.out.println("Enter number " + counter);
           intSides = sc.nextInt();
       }
    
       counter++;
       return intSides;
    }

Ivan Jozsef Balazs - does that mean I have to stop the user from entering any negative numbers?  

[Knute Snortum]

Bod MacNeil wrote:I thought my while loop would run at least once as sc.hasNextInt() should return false as nothing is passed to it?

No, it will block.  That is, it will wait forever for input, since it can't determine the correct value to return without input.

Would a do while loop be better?  I tried that also and it didn't work.

This is a situation that is tailor made for a do loop.  

So what did you try and how specifically didn't it work?

does that mean I have to stop the user from entering any negative numbers?  

I would think so.  I don't think a negative length is legal.

[Campbell Ritchie]

Bod MacNeil wrote:. . .

// ...
       while(!sc.hasNextInt()){
           System.out.println("Enter number " + counter);
           intSides = sc.nextInt();
       }
// ...
    }

That form of loop looks incorrect to me, and I think it will not work.

Ivan Jozsef Balazs - does that mean I have to stop the user from entering any negative numbers?  

If you follow my suggestion of creating a utility class, you can overload the netxInt method to return only values in a particular range. I showed you part of that method yesterday well over a week ago.