Chapter 1: Declaration and Access control

Question 1

What are valid starting characters for identifiers?

Answer 1

letters, $, _

Question 2

True or False: foo and FOO are the same identifiers.

Answer 2

False

Question 3

Name the valid getter methods for a boolean.

Answer 3

getBoolean, isBoolean

Question 4

Name the JavaBean methods for MyListener.

Answer 4

addMyListener(MyListener listener)

removeMyListener(MyListener listener)

Question 5

Name the access modifiers starting with the most restrictive

Answer 5

private -> class only
default -> package only 
protected -> inheritance and package only
public -> anywhere

Question 6

What are the non-access modifiers for classes?

Answer 6

final, abstract, strictfp

Question 7

What is wrong?
class MyObject {
    public abstract void myMethod();
}

Answer 7

Both the class and the method should have a abstract modifier.

Question 8

True or False: All methods in an interface are public abstract.

Answer 8

True

Question 9

What are variables declared in a interface?

Answer 9

public static final

Question 10

What is wrong?
class foo {
   void doStuff() {
      private final int x = 7;
   }
}

Answer 10

Access modifiers can’t be used in conjuction with local variables.

Final is the only non-acces modifier that can be used

Question 11

Synchronized key word can be applied to:

Answer 11

methods & code-blocks

Question 12

Which of these methods are valid var-arg methods:

1: void doStuff(int x…)
2: void doStuff(int… x, int… y)
3. void doStuff(int… x)
4. void doStuff(int… x, int y)
5. void doStuff(int y, Animal… a)

Answer 12

3 & 5

Question 13

Name the 8 primitives

Answer 13

byte, short, int, long, float, double, boolean, char

Question 14

Describe the integer types from small to large

Answer 14

byte: 8 bits (2^7) (we lose one bit for the sign (-/+))
short: 16 bits (2^15)
int: 32 bits (2^31)
long: 64 bits (2^63)

float: 32 bits
double: 64 bits

Question 15

Describe the max range for a char

Answer 15

char: 16 bits
No signing bit
2^16 = 0-65535

Question 16

What are valid non-access modifiers for instance variables?

Answer 16

final and transient

Question 17

What is wrong?

public class MyClass {
   public void doStuff() {
      int a;
      a++;
   }
}

Answer 17

local variables should be initialized (don’t get a default value)

Question 18

What is shadowing?

Answer 18

declaring a local variable with the same name as an instance variable.

Question 19

Name the two ways of declaring an array.

Answer 19

type[] key (for example: int[] a)

type key[] (for example: int a[])

Question 20

What does the transient keyword?

Answer 20

exclude a instance variable from serialization

Question 21

What are valid acces modifiers for classes?

Answer 21

pulbic and default

Question 22

What will be the result?

class TestClass
{
   int i = getInt();
   int k = 20;
   public int getInt() {  return k+1;  }
   public static void main(String[] args)
   {
      TestClass t = new TestClass();
      System.out.println(t.i+"  "+t.k);
   }
}

Answer 22

Answer: 1 20 is printed

First the memory is allocated for TestClass Object referred to by variable t. Here, all the variables get their default values. so i and k are both zeros.
Now, the initialilization starts. To initialize i it calls getInt(). This method returns k+1. At this point of time ‘k’ is 0. (because it has not been initialized yet.) so it returns 1. Next, k is init’ed to 20. So, 1 20 is printed.
Note that had k = 20; occured before i = getInt(); it would have printed 21 20.