EnumSet.of(K, K, K, K) in Java

EnumSet.of(K, K, K, K): This method is available in java.util.EnumSet class of Java.

Syntax:

<K> EnumSet<Colour> java.util.EnumSet.of(K e1, K e2, K e3, K e4)

This method takes four arguments. This method creates an enum set initially containing the specified elements.

Parameters: Four parameters are required for this method.

e1: an element that this set is to contain initially.

e2: another element that this set is to contain initially.

e3: another element that this set is to contain initially.

e4: another element that this set is to contain initially.

Returns: an enum set initially containing the specified elements.

Throws:

NullPointerException - if any parameters are null

Approach 1: When no exception

Java

import java.util.EnumSet;

public class EnumSetof5 {
    public enum Colour {
        RED, GREEN, YELLOW, ORANGE
    };

    public static void main(String[] args) {

        EnumSet<Colour> enumSet;

        Colour e4 = Colour.YELLOW;
        enumSet = EnumSet.of(Colour.GREEN, Colour.ORANGE, 
                                 Colour.RED, e4);
        System.out.println(enumSet);

    }
}

Output:

[RED, GREEN, YELLOW, ORANGE]

Approach 2: NullPointerException 

Java

import java.util.EnumSet;

public class EnumSetof5 {
    public enum Colour {
        RED, GREEN, YELLOW, ORANGE
    };

    public static void main(String[] args) {

        EnumSet<Colour> enumSet;

        Colour e4 = null;
        enumSet = EnumSet.of(Colour.GREEN, Colour.ORANGE,
                            Colour.RED, e4);
        System.out.println(enumSet);

    }
}

Output:

Exception in thread "main" java.lang.NullPointerException: Cannot invoke "Object.getClass()" because "e" is null
	at java.base/java.util.EnumSet.typeCheck(EnumSet.java:397)
	at java.base/java.util.RegularEnumSet.add(RegularEnumSet.java:162)
	at java.base/java.util.RegularEnumSet.add(RegularEnumSet.java:36)
	at java.base/java.util.EnumSet.of(EnumSet.java:289)