The toArray(T[]) method method of TreeSet class in Java is used to form an array of the same elements as that of the TreeSet. It returns an array containing all of the elements in this TreeSet in the correct order; the run-time type of the returned array is that of the specified array. If the TreeSet fits in the specified array, it is returned therein. Otherwise, a new array is allocated with the run time type of the specified array and the size of this TreeSet.
If the TreeSet fits in the specified array with room to spare (i.e., the array has more elements than the TreeSet), the element in the array immediately following the end of the TreeSet is set to null. (This is useful in determining the length of the TreeSet only if the caller knows that the TreeSet does not contain any null elements.)
Syntax:
public <T> T[] toArray(T[] a)
Parameters: The method accepts one parameter arr[] which is the array into which the elements of the TreeSet are to be stored, if it is big enough; otherwise, a new array of the same runtime type is allocated for this purpose.
Return Value: The method returns an array containing the elements similar to the TreeSet.
Exception: The method might throw two types of exception:
- ArrayStoreException: When the mentioned array is of the different type and is not able to compare with the elements mentioned in the TreeSet.
- NullPointerException: If the array is Null, then this exception is thrown.
Below program illustrates the working of the TreeSet.toArray(arr[]) method.
Program 1: When array is of the size of TreeSet
// Java code to illustrate toArray(arr[]) import java.util.*; public class TreeSetDemo { public static void main(String args[]) { // Creating an empty TreeSet TreeSet<String> set = new TreeSet<String>(); // Use add() method to add // elements into the TreeSet set.add("Welcome"); set.add("To"); set.add("Geeks"); set.add("For"); set.add("Geeks"); // Displaying the TreeSet System.out.println("The TreeSet: " + set); // Creating the array and using toArray() String[] arr = new String[5]; arr = set.toArray(arr); // Displaying arr System.out.println("The arr[] is:"); for (int j = 0; j < arr.length; j++) System.out.println(arr[j]); }} |
The TreeSet: [For, Geeks, To, Welcome] The arr[] is: For Geeks To Welcome null
Program 2: When array is less than the size of TreeSet
// Java code to illustrate toArray(arr[]) import java.util.*; public class TreeSetDemo { public static void main(String args[]) { // Creating an empty TreeSet TreeSet<String> set = new TreeSet<String>(); // Use add() method to add // elements into the TreeSet set.add("Welcome"); set.add("To"); set.add("Geeks"); set.add("For"); set.add("Geeks"); // Displaying the TreeSet System.out.println("The TreeSet: " + set); // Creating the array and using toArray() String[] arr = new String[1]; arr = set.toArray(arr); // Displaying arr System.out.println("The arr[] is:"); for (int j = 0; j < arr.length; j++) System.out.println(arr[j]); }} |
The TreeSet: [For, Geeks, To, Welcome] The arr[] is: For Geeks To Welcome
Program 3: When array is more than the size of TreeSet
// Java code to illustrate toArray(arr[]) import java.util.*; public class TreeSetDemo { public static void main(String args[]) { // Creating an empty TreeSet TreeSet<String> set = new TreeSet<String>(); // Use add() method to add // elements into the TreeSet set.add("Welcome"); set.add("To"); set.add("Geeks"); set.add("For"); set.add("Geeks"); // Displaying the TreeSet System.out.println("The TreeSet: " + set); // Creating the array and using toArray() String[] arr = new String[10]; arr = set.toArray(arr); // Displaying arr System.out.println("The arr[] is:"); for (int j = 0; j < arr.length; j++) System.out.println(arr[j]); }} |
The TreeSet: [For, Geeks, To, Welcome] The arr[] is: For Geeks To Welcome null null null null null null
Program 4: To demonstrate NullPointerException
// Java code to illustrate toArray(arr[]) import java.util.*; public class TreeSetDemo { public static void main(String args[]) { // Creating an empty TreeSet TreeSet<String> set = new TreeSet<String>(); // Use add() method to add // elements into the TreeSet set.add("Welcome"); set.add("To"); set.add("Geeks"); set.add("For"); set.add("Geeks"); // Displaying the TreeSet System.out.println("The TreeSet: " + set); try { // Creating the array String[] arr = null; // using toArray() // Since arr is null // Hence exception will be thrown arr = set.toArray(arr); // Displaying arr System.out.println("The arr[] is:"); for (int j = 0; j < arr.length; j++) System.out.println(arr[j]); } catch (Exception e) { System.out.println("Exception: " + e); } }} |
The TreeSet: [For, Geeks, To, Welcome] Exception: java.lang.NullPointerException
