Useful Methods for Lists

Java provides the methods for creating a list from an array, for sorting a list, and finding maximum and minimum element in a list, and for shuffling a list. Often you need to create an array list from an array of objects or vice versa. You can write the code using a loop to accomplish this, but an easy way is to use the methods in the Java API. Here is an example to create an array list from an array:

String[] array = {"red", "green", "blue"};
ArrayList<String> list = new ArrayList<>(Arrays.asList(array));

The static method asList in the Arrays class returns a list that is passed to the ArrayList constructor for creating an ArrayList. Conversely, you can use the following code to create an array of objects from an array list.

String[] array1 = new String[list.size()];
list.toArray(array1);

Invoking list.toArray(array1) copies the contents from list to array1. If the elements in a list are comparable such as integers, double, or strings, you can use the static sort method in the java.util.Collections class to sort the elements. Here are examples:

Integer[] array = {3, 5, 95, 4, 15, 34, 3, 6, 5};
ArrayList<Integer> list = new ArrayList<>(Arrays.asList(array));
java.util.Collections.sort(list);
System.out.println(list);

You can use the static max and min in the java.util.Collections class to return the maximum and minimal element in a list. Here are examples:

Integer[] array = {3, 5, 95, 4, 15, 34, 3, 6, 5};
ArrayList<Integer> list = new ArrayList<>(Arrays.asList(array));
System.out.println(java.util.Collections.max(list));
System.out.println(java.util.Collections.min(list));

You can use the static shuffle method in the java.util.Collections class to perform a random shuffle for the elements in a list. Here are examples:

Integer[] array = {3, 5, 95, 4, 15, 34, 3, 6, 5};
ArrayList<Integer> list = new ArrayList<>(Arrays.asList(array));
java.util.Collections.shuffle(list);
System.out.println(list);