SCJP : Type Safe Enum Mock Exam Practice Questions

Questions no -1 
What is the output for the below code ?

public enum Test {
	BREAKFAST(7, 30), LUNCH(12, 15), DINNER(19, 45);
	
	private int hh;

	private int mm;

	Test(int hh, int mm) {
		assert (hh >= 0 && hh <= 23) : "Illegal hour.";
		assert (mm >= 0 && mm <= 59) : "Illegal mins.";
		this.hh = hh;
		this.mm = mm;
	}

	public int getHour() {
		return hh;
	}

	public int getMins() {
		return mm;
	}
	
	public static void main(String args[]){
		Test t =  new BREAKFAST;
		System.out.println(t.getHour() +":"+t.getMins());
	}
}




options
A)7:30
B)Compile Error - an enum cannot be instantiated using the new operator.
C)12:50
D)19:45

Correct answer is : B

Explanations : As an enum cannot be instantiated using the new operator, the constructors cannot be called explicitly.
You have to do like 
Test t =  BREAKFAST;

Questions no -2 
What is the output for the below code ?

public class Test {
	enum Day {
		MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY, SUNDAY
	}
	enum Month {
		JAN, FEB
	}

	public static void main(String[] args) {

		int[] freqArray = { 12, 34, 56, 23, 5, 13, 78 };

		// Create a Map of frequencies
		Map ordinaryMap = new HashMap();
		for (Day day : Day.values()) {
			ordinaryMap.put(day, freqArray[day.ordinal()]);
		}
		

		// Create an EnumMap of frequencies
		EnumMap frequencyEnumMap = new EnumMap(ordinaryMap);

		// Change some frequencies
		frequencyEnumMap.put(null, 100);
		
		System.out.println("Frequency EnumMap: " + frequencyEnumMap);

		
	}

}


options
A)Frequency EnumMap: {MONDAY=12, TUESDAY=34, WEDNESDAY=56, THURSDAY=23, FRIDAY=5, SATURDAY=13, SUNDAY=78}
B)Compile Error 
C)NullPointerException
D)Frequency EnumMap: {MONDAY=100, TUESDAY=34, WEDNESDAY=56, THURSDAY=23, FRIDAY=5, SATURDAY=13, SUNDAY=123}

Correct answer is : C

Explanations : The null reference as a key is NOT permitted.

Questions no -3 
public class EnumTypeDeclarations {
	
	public void foo() {
		
		enum SimpleMeal { 
			BREAKFAST, LUNCH, DINNER 
		}
	}
}

Is the above code Compile without error ?


options
A)Compile without error
B)Compile with error
C)Compile without error but Runtime Exception
D)Compile without error but Enum Exception

Correct answer is : B

Explanations :
An enum declaration is a special kind of class declaration:
a) It can be declared at the top-level and as static enum declaration. 
b) It is implicitly static, i.e. no outer object is associated with an enum constant. 
c) It is implicitly final unless it contains constant-specific class bodies, but it can implement interfaces. 
d) It cannot be declared abstract unless each abstract method is overridden in the constant-specific class body of every enum constant. 
e) Local (inner) enum declaration is NOT OK! 

Here in
public void foo() {
		
		enum SimpleMeal { 
			BREAKFAST, LUNCH, DINNER 
		}
	}

enum declaration is local within method so compile time error.

Questions no -4 
What is the output for the below code ?

public enum Test {
	int t;
	BREAKFAST(7, 30), LUNCH(12, 15), DINNER(19, 45);
	
	private int hh;

	private int mm;

	Test(int hh, int mm) {
		assert (hh >= 0 && hh <= 23) : "Illegal hour.";
		assert (mm >= 0 && mm <= 59) : "Illegal mins.";
		this.hh = hh;
		this.mm = mm;
	}

	public int getHour() {
		return hh;
	}

	public int getMins() {
		return mm;
	}
	
	public static void main(String args[]){
		Test t =  BREAKFAST;
		System.out.println(t.getHour() +":"+t.getMins());
	}
}




options
A)7:30
B)Compile Error 
C)12:15
D)19:45

Correct answer is : B

Explanations : The enum constants must be declared before any other declarations in an enum type.
In this case compile error because of declaration int t; before enum declaration.