Merges two lists into one list
Formatting

Now let's talk about formatting. Your code is hard to read. Format it. Done.

Actually, if you want some tips:


import java.util.*;
public class MergeTwoSortedLists {
    public static void main(String[] args) 
    {



These lines of code have a couple of problems:

Line 1-2: Space between import statements and class declaration

Line 2-3: Space between class declaration and first line of code inside class

Line 3-4: Java conventions require that braces are on the same line as declaration

Result:

import java.util.*;

public class MergeTwoSortedLists {

    public static void main(String[] args) {


This code:


 java.util.Scanner input = new java.util.Scanner(System.in);

 // Enter values for list1
 System.out.println("Enter the amount of numbers in the first list:");
 // Assign user defined length to the array
 int lengthOfArray = input.nextInt();
 int[] list1 = new int[lengthOfArray];

 // i increments and the user values are assigned to the array until the length is exceeded  
 System.out.println("Enter " + list1.length + " values: ");
 for (int i = 0; i &lt; list1.length; i++) // line 11
  list1[i] = input.nextInt();


 // Enter values for list2
 System.out.println("Enter the amount of numbers in the second list:");
 // Assign user defined length to the array
 int lengthOfArray2 = input.nextInt();
 int[] list2 = new int[lengthOfArray2];

 // i increments and the user values are assigned to the array until the length is exceeded
 System.out.println("Enter " + list2.length + " values: ");
 for (int i = 0; i &lt; list2.length; i++) // line 23
  list2[i] = input.nextInt();

 // Lists one and two are merged into one list
 int[] list3 = merge(list1, list2);
 // Sorts the lists in numerical order
 Arrays.sort(list3);
 // This accesses the actual user defined integers and not their locations, printing them in an assorted array
 System.out.println("The merged list is: " +Arrays.toString(list3));



all share a problem. That problem is that you are indenting it by only 1 space, Java conventions recommend 4-space tabs, or just 4 spaces.

Some other things:

Line 11 (as marked by comment): ALWAYS put braces to group if, else, while, do-while, for, and similar statements. Here is why.

Line 13 or 14: Two empty lines won't improve readability. Remove one.

Line 23 (as marked by a comment): Same thing as Line 11

Last line: Space before and after +

Result:

    java.util.Scanner input = new java.util.Scanner(System.in);

    // Enter values for list1
    System.out.println("Enter the amount of numbers in the first list:");
    // Assign user defined length to the array
    int lengthOfArray = input.nextInt();
    int[] list1 = new int[lengthOfArray];

    // i increments and the user values are assigned to the array until the length is exceeded  
    System.out.println("Enter " + list1.length + " values: ");
    for (int i = 0; i &lt; list1.length; i++) {
        list1[i] = input.nextInt();
    }

    // Enter values for list2
    System.out.println("Enter the amount of numbers in the second list:");
    // Assign user defined length to the array
    int lengthOfArray2 = input.nextInt();
    int[] list2 = new int[lengthOfArray2];

    // i increments and the user values are assigned to the array until the length is exceeded
    System.out.println("Enter " + list2.length + " values: ");
    for (int i = 0; i &lt; list2.length; i++) {
        list2[i] = input.nextInt();
    }

    // Lists one and two are merged into one list
    int[] list3 = merge(list1, list2);
    // Sorts the lists in numerical order
    Arrays.sort(list3);
    // This accesses the actual user defined integers and not their locations, printing them in an assorted array
    System.out.println("The merged list is: " + Arrays.toString(list3));


Here:


public static int[] merge(int[] list1, int[] list2)
{
    int[] list3 = new int[list1.length + list2.length];
    // Both p and i increment, and list 3 is assigned the user defined integers from both list 1 and 2
    for (int i = 0, p=0 ; i &lt; list1.length || i &lt; list2.length ; i++) {
        if (i &lt; list1.length) {
            list3[p++] = list1[i];
        }
        if (i &lt; list2.length) {
            list3[p++] = list2[i];
        }
    }
    return list3;
    // line 15
}



Looks pretty good, but some points:

Line 1: Space between methods

Line 1-2: Java conventions require that braces are on the same line as declaration

Line 4: Space before and after =
Line 4: Usually no space is required before ;

Line 15: Extra newline at the end of the method is not necessary

Result:

public static int[] merge(int[] list1, int[] list2) {
    int[] list3 = new int[list1.length + list2.length];
    // Both p and i increment, and list 3 is assigned the user defined integers from both list 1 and 2
    for (int i = 0, p = 0; i &lt; list1.length || i &lt; list2.length; i++) {
        if (i &lt; list1.length) {
            list3[p++] = list1[i];
        }
        if (i &lt; list2.length) {
            list3[p++] = list2[i];
        }
    }
    return list3;
}


Review


import java.util.*;



Never import an entire package, even if you are using a lot of the package. In this case, all you need is `Scanner, so that's even worse.

import java.util.Scanner;


is what you should do.


java.util.Scanner input = new java.util.Scanner(System.in);



Why are you using the full name when you just imported it?

Scanner input = new Scanner(System.in);


Now, to your merge method:


The method should be private
Since you are sorting the array anyways, it is more efficient to sort the arrays, then merge them, like the final step of merge sort:

private static int[] merge(int[] array1, int[] array2) {
    int length1 = array1.length;
    int length2 = array2.length;

    int[] array = new int[length1 + length2];

    int index1 = 0;
    int index2 = 0;

    while (index1 &lt; length1 &amp;&amp; index2 &lt; length2) {
        array[index1 + index2] = array1[index1] &lt; array2[index2]
                ? array1[index1++]
                : array2[index2++];
    }
    while (index1 &lt; length1) {
        array[index1 + index2] = array1[index1++];
    }
    while (index2 &lt; length2) {
        array[index1 + index2] = array2[index2++];
    }
    return array;
}



Final Code:

import java.util.Scanner;

public class MergeTwoSortedLists {

    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);

        // Enter values for list1
        System.out.println("Enter the amount of numbers in the first list:");
        // Assign user defined length to the array
        int lengthOfArray = input.nextInt();
        int[] list1 = new int[lengthOfArray];

        // i increments and the user values are assigned to the array until the length is exceeded  
        System.out.println("Enter " + list1.length + " values: ");
        for (int i = 0; i &lt; list1.length; i++) {
            list1[i] = input.nextInt();
        }

        // Enter values for list2
        System.out.println("Enter the amount of numbers in the second list:");
        // Assign user defined length to the array
        int lengthOfArray2 = input.nextInt();
        int[] list2 = new int[lengthOfArray2];

        // i increments and the user values are assigned to the array until the length is exceeded
        System.out.println("Enter " + list2.length + " values: ");
        for (int i = 0; i &lt; list2.length; i++) {
            list2[i] = input.nextInt();
        }
        // Sorts the lists in numerical order
        Arrays.sort(list1);
        Arrays.sort(list2);

        // Lists one and two are merged into one list
        int[] list3 = merge(list1, list2);
        // This accesses the actual user defined integers and not their locations, printing them in an assorted array
        System.out.println("The merged list is: " + Arrays.toString(list3));
    }

    private static int[] merge(int[] array1, int[] array2) {
        int length1 = array1.length;
        int length2 = array2.length;

        int[] array = new int[length1 + length2];

        int index1 = 0;
        int index2 = 0;

        while (index1 &lt; length1 &amp;&amp; index2 &lt; length2) {
            array[index1 + index2] = array1[index1] &lt; array2[index2]
                    ? array1[index1++]
                    : array2[index2++];
        }
        while (index1 &lt; length1) {
            array[index1 + index2] = array1[index1++];
        }
        while (index2 &lt; length2) {
            array[index1 + index2] = array2[index2++];
        }
        return array;
    }

}