How to solve variable might not have been initialized error

Question

I started studying for an exam and doing some practice programs with methods, and my mind is coming to a blank currently. I would like to know how I can initialize n1, n2, n3, and n4. I set them to 0 but the return statement returned only 0s.

public class LargestOfIntegers2
{
    public static int findLargest(int n1, int n2, int n3, int n4)
    {
        Scanner scan = new Scanner(System.in);
        System.out.print("Enter the first integer --> ");
        n1 = scan.nextInt();
        System.out.print("Enter the second integer --> ");
        n2 = scan.nextInt();    
        System.out.print("Enter the third integer --> ");
        n3 = scan.nextInt();    
        System.out.print("Enter the fourth integer --> ");
        n4 = scan.nextInt();    

        if(n1>n2 && n1 > n3 && n1 > n4)
            return n1;
        else if(n2 > n1 && n2 > n3 && n2 > n4)
           return n2;
        else if(n3>n1 && n3>n2 && n3>n4)
            return n3;
        else
            return n4;
    }

    public static void main(String[] args) {
        int n1, n2, n3, n4;

        findLargest(n1, n2, n3, n4);
        if(n1>n2 && n1 > n3 && n1 > n4)
            System.out.println("Out of the numbers " + n1 + ", " + n2 + ", " + n3 + ", " + n4 + ", the largest integer is " + n1);
        else if(n2 > n1 && n2 > n3 && n2 > n4)
            System.out.println("Out of the numbers " + n1 + ", " + n2 + ", " + n3 + ", " + n4 + ", the largest integer is " + n2);
        else if(n3>n1 && n3>n2 && n3>n4)
            System.out.println("Out of the numbers " + n1 + ", " + n2 + ", " + n3 + ", " + n4 + ", the largest integer is " + n3);
        else
            System.out.println("Out of the numbers " + n1 + ", " + n2 + ", " + n3 + ", " + n4 + ", the largest integer is " + n4);

    }
}

Answer 1

The variables n1 through n4 will be set in the findLargest function but only the local copies of them, the changes will never be "echoed" back to the main function. That's your primary problem since the variables in main are not being set because of that.

You would be better off asking for each variable in a function and returning it, then using findLargest correctly by getting the return value. That would go something like:

import java.util.Scanner;

public class Test {
    public static int getNum(Scanner sc, String desc) {
        System.out.print("Enter the " + desc + " integer --> ");
        return sc.nextInt();
    }

    public static int findLargest(int n1, int n2, int n3, int n4) {
        if (n1 >= n2 && n1 >= n3 && n1 >= n4)
            return n1;
        if (n2 >= n3 && n2 >= n4)
           return n2;
        if (n3 >= n4)
            return n3;
        return n4;
    }

    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        int a = getNum(scan, "first");
        int b = getNum(scan, "second");
        int c = getNum(scan, "third");
        int d = getNum(scan, "fourth");

        int x = findLargest(a, b, c, d);
        System.out.println("max(" + a + "," + b + "," + c + "," + d + ") = " + x);
    }
}

You can see I've also made changes to the findLargest function to minimise comparisons. For example, if you get through the first if statement without returning, you know that n1 is irrelevant to further comparisons since it's smaller than at least one other value.

Answer 2

The main reason your code didn't work:

public static void main(String[] args) {
    int n1, n2, n3, n4;

    findLargest(n1, n2, n3, n4);    <--- YOU DID NOT STORE THE RETURNED VALUE
    if(n1>n2 && n1 > n3 && n1 > n4)
        System.out.println("Out of the numbers " + n1 + ", " + n2 + ", " + n3 + ", " + n4 + ", the largest integer is " + n1);
    else if(n2 > n1 && n2 > n3 && n2 > n4)
        System.out.println("Out of the numbers " + n1 + ", " + n2 + ", " + n3 + ", " + n4 + ", the largest integer is " + n2);
    else if(n3>n1 && n3>n2 && n3>n4)
        System.out.println("Out of the numbers " + n1 + ", " + n2 + ", " + n3 + ", " + n4 + ", the largest integer is " + n3);
    else
        System.out.println("Out of the numbers " + n1 + ", " + n2 + ", " + n3 + ", " + n4 + ", the largest integer is " + n4);

}

Do either:

//prompt user input for n1, n2, n3, n4 first
System.out.println(findLargest(n1,n2,n3,4));

OR

//prompt user input for n1, n2, n3, n4 first
int largest = findLargest(n1,n2,n3,n4);
System.ouot.println(largest);

I am sure this will make your code work. Of course, instead of prompting the user input in the method, you should prompt it outside the method, before you call the method.

---

Explanation of how Java method passes its value:

public static void main(String[] args)
{
    int n = 100;
    someMethod(n);
    System.out.println(n); //n will still be 100;
}

public static void someMethod(int n1)
{
    n1 = 999;
}

Why is n in the main still 100, and not 999. This is because Java passes everything by value. For primitive types, the value passed is the actual value itself. Meaning that a copy of the actual value will be passed in to the method. A copy was made. Thus n1(scope:someMethod) is just a copy of n(scope:main). Changes on n1 do not affect n.

---

Something extra for you:

If you are passing in the 4 variables n1, n2, n3, n4. Why are you asking the user to input the 4 values once more in your method?

Doing so will "void" the values of n1, n2, n3, n4 passed in from the caller of the method.

By the way there are many much simpler ways to implement this. By not touching on arrays, you can simply do this:

public static int findLargest(int n1, int n2, int n3, int n4)
{
    return Math.max(Math.max(n1,n2), Math.max(n3,n4));
}

Answer 3

this is what your code will do: this will get new n1 and n2 and n3 and n4 and set them equal to the values you pass

  public static int findLargest(int n1, int n2, int n3, int n4){
 {

you pass an uninitialized value so they are uninitialized you then initialize them with the user input (THIS WONT CHANGE ANYTHING OUTSIDE OF THIS METHOD AS YOUR VARIABLES ARE LOCAL) you then find the biggest and return it YOUR CODE DOESN'T STORE THIS VALUE ANYWHERE

 int thelargest=findLargest(n1, n2, n3, n4);

would store it

you then try and compare UNINITIALIZED INTS as the method findlargest can't see n1 n2 n3 n4 as there is no pass by refference to fix your code to do what i think you want do this

 static int n1,n2,n3,n4;
  public static void findLargest()

{
Scanner scan = new Scanner(System.in);
System.out.print("Enter the first integer --> ");
n1 = scan.nextInt();
System.out.print("Enter the second integer --> ");
n2 = scan.nextInt();    
System.out.print("Enter the third integer --> ");
n3 = scan.nextInt();    
System.out.print("Enter the fourth integer --> ");
n4 = scan.nextInt();    
//nothing is listening for these numbers anyway why bother with it
 // if(n1>n2 && n1 > n3 && n1 > n4)
 //   return n1;
 // else if(n2 > n1 && n2 > n3 && n2 > n4)
  // return n2;
 // else if(n3>n1 && n3>n2 && n3>n4)
//      return n3;
 // else
 //    return n4;
}

public static void main(String[] args) {
//int n1, n2, n3, n4;

findLargest();
if(n1>n2 && n1 > n3 && n1 > n4)
    System.out.println("Out of the numbers " + n1 + ", " + n2 + ", " + n3 + ", " + n4 + ", the largest integer is " + n1);
else if(n2 > n1 && n2 > n3 && n2 > n4)
    System.out.println("Out of the numbers " + n1 + ", " + n2 + ", " + n3 + ", " + n4 + ", the largest integer is " + n2);
else if(n3>n1 && n3>n2 && n3>n4)
    System.out.println("Out of the numbers " + n1 + ", " + n2 + ", " + n3 + ", " + n4 +   ", the largest integer is " + n3);
else
    System.out.println("Out of the numbers " + n1 + ", " + n2 + ", " + n3 + ", " + n4         +    ", the largest integer is " + n4);

}

}