Java Objects - Medium Practice Quiz

Which statement best describes a parameterised constructor in OOP?

• A method that returns a value to the caller
• A special method that sets initial field values using arguments during object creation
• A static initializer that runs once per class
• Any method that accepts parameters
• A method that only draws on screen

Answer explanation

A parameterised constructor takes arguments and assigns initial values to fields when an object is created.

Given: String s = "0123456789"; System.out.println(s.substring(4)); What is printed?

• 456789
• 123
• 3456789
• 56789
• 1234

Answer explanation

substring(4) returns characters from index 4 to end, yielding 456789.

Given: String s = "0123456789"; System.out.println(s.substring(s.lastIndexOf('3'), s.indexOf('8'))); What is printed?

• 345678
• 34567
• 45678
• 34
• 567

Answer explanation

lastIndexOf('3') is 3, indexOf('8') is 8; substring(3,8) gives 34567.

Given:

String s = "abcabc";

System.out.println(s.lastIndexOf("abc", 2));

System.out.println(s.substring(3, 3).length());

What is printed on two lines?

• 3 and 0
• 0 and 0
• 0 and 3
• -1 and 0
• 3 and 3

Answer explanation

lastIndexOf("abc", 2) searches up to index 2 inclusive, finds abc at 0; substring(3,3) is empty, length is 0.

Which option correctly identifies a parameterised method that also returns a value?

• void makeVisible()
• int moveHorizontal()
• int moveHorizontal(int distance)
• void changeColor(String color)
• void moveDown()

Answer explanation

moveHorizontal(int distance) both takes a parameter and could be defined to return an int; among given options, it matches signature of parameterised and returning method.

Consider class Account { int balance; Account(int initial){ balance = initial + 50; } } After Account a = new Account(150); what is a.balance?

• 0
• 150
• 50
• 200
• 100

Answer explanation

The parameterised constructor sets balance = initial + 50, so 150 + 50 = 200.

In Circle, which method changes position based on caller-provided information?

• moveRight()
• moveDown()
• moveHorizontal(int distance)
• makeVisible()
• draw()

Answer explanation

moveHorizontal changes xPosition using the distance provided by the caller.

Given

class Counter { int count; Counter(int c){ this.count = c; } Counter inc(){ count++; return this; } Counter reset(){ return new Counter(0); } }

and code:

Counter a = new Counter(1); Counter b = a.inc().reset(); a.inc(); System.out.println(a.count + " " + b.count);

What is printed?

• 2 0
• 2 1
• 3 0
• 3 1
• 1 0

Answer explanation

a starts 1; a.inc() makes a.count=2, returns a; reset() creates new Counter(0) assigned to b; a.inc() again makes a.count=3. Prints 3 0.

Which statement is true about a method that returns a value compared to a void method?

• It cannot modify object state
• It must be static
• It can both compute a result to return and modify state
• It cannot have parameters
• It must have the same name as the class

Answer explanation

A returning method may modify state and also return a computed result; return type does not restrict state changes.

What is the output? StringBuilder sb = new StringBuilder("Hi"); sb.append("-").append(2).insert(0, "_"); System.out.println(sb.toString());

• _Hi-2
• Hi-2_
• Hi-_2
• _2-Hi
• Hi_ -2

Answer explanation

Start Hi, append -2 gives Hi-2, insert at 0 "_" results in _Hi-2.