SCJP Basic 4 — Questions and Answers
Question 1: What happens when you assign a larger numeric type to a smaller one without casting in Java?
- Java auto-narrows it
- Compile-time error (Correct answer)
- Runtime exception
- Data is silently truncated
Correct answer: Compile-time error
Narrowing conversions require an explicit cast; without one, the compiler produces an error.
Question 2: Which loop is guaranteed to execute its body at least once?
- for
- while
- do-while (Correct answer)
- enhanced for
Correct answer: do-while
A do-while loop checks its condition after executing the body, so it always runs at least once.
Question 3: What is the output of: System.out.println("Hello" + 1 + 2);?
- Hello3
- Hello12 (Correct answer)
- 3Hello
- Compile error
Correct answer: Hello12
String concatenation is left-to-right; "Hello" + 1 = "Hello1", then "Hello1" + 2 = "Hello12".
Question 4: Which of the following is true about Java's 'break' statement in a switch block?
- It exits the entire program
- It skips to the next case without executing it
- It prevents fall-through to the next case (Correct answer)
- It is required in every case
Correct answer: It prevents fall-through to the next case
Without break, execution falls through to subsequent cases; break exits the switch block.
Question 5: What is the purpose of the 'this' keyword in Java?
- It refers to the parent class
- It refers to the current object instance (Correct answer)
- It creates a new object
- It refers to the class itself
Correct answer: It refers to the current object instance
The 'this' keyword is a reference to the current object within an instance method or constructor.
Question 6: Which of the following correctly defines a constructor in Java?
- void MyClass() {}
- MyClass MyClass() {}
- MyClass() {} (Correct answer)
- static MyClass() {}
Correct answer: MyClass() {}
A constructor has the same name as the class and no return type, not even void.
Question 7: What is method overloading in Java?
- Providing a new implementation for a parent class method
- Defining multiple methods with the same name but different parameter lists (Correct answer)
- Making a method run faster
- Preventing a method from being overridden
Correct answer: Defining multiple methods with the same name but different parameter lists
Overloading lets you define multiple methods with the same name differing in number or type of parameters.
SCJP Basic 4
What happens when you assign a larger numeric type to a smaller one without casting in Java?