1. Java 7: Language Enhancements

Question 1

What are the two things you need to know for using a String in a switch expression?

Answer 1

• check for null value

- the value is case-sensitive (fe: wOrD does not match a case WORD)

Question 2

What are the integer literals?

Answer 2

Decimal: 26
Hexadecimal: 0x1A
Binary: 0b11010 (new in Java 7)

Question 3

What is the result of the following:
float f1 = 0b0001;
float f2 = 0B0001F;

Answer 3

Compilation fails, Binary literal (new in Java 7) can only be used with integer type (byte, short, int, long)

Question 4

Which of these are valid?

1. int x1 = 5_2;
2. float f2 = 3_.1415F;
3. long l3 = 99_99_L;
4. int x4 = 0x5_2;
5. int x5 = 0B0_0_0;
6. int x6 = 52_;
7. int x7 = 0_x52;
8. int x8 = _52;

Answer 4

Valid: 1,4,5

Invalid:

2: underscore next to the decimal point
3: underscore next to the L.
6: underscore at the end of the literal.
7: underscore between the 0 and x of the hexadecimal literal.
8: not a integer literal but an identifier

Question 5

What are the requirements for a resource that can be used in a try-with-resource construction?

Answer 5

Object (the resource) must implement the auto-closable interface (or the closable interface with extends the autoclosable interface.)

Question 6

What is the difference between the AutoClosable and the Closable interface?

Answer 6

The void close() method of the AutoClosable throws an Exception while the Closable’s close() method trhwos an IOException.

Question 7

What is the result of the following method, considering the first line of the file contains the text “Hello World”.

public void main(String args[]) {
   try(BufferedReader br = new BufferedReader(new 
              FileReader("text.txt))) {
      return br.readLine();
   }
}

Answer 7

Compile error!

BufferedReader implements the AutoClosable interface, the both the close method and the readLine call could throw an IOException. The IOException is not declared in the method signature or as a catch clause.

Question 8

True or False:

A Try-with-resource construction can only be used with one Resource (object that implements AutoClosable interface).

Answer 8

False

You declare en initialize multiple resources seperated by semicolons. The resources will be closed in the opposite direction in which they are created.

Question 9

True or False:

The catch are finally block are optional when using the try-with-resource construction.

Answer 9

True

The catch and finally are optional. But they can be declared. The catch and finnaly block are run after the resources declared have been closed.

Question 10

True or False:
When using the try-with-resource construction you need to define at least one catch clause catching a IOException/Exception or the method signature should have a throws clause.

Answer 10

True

The creation could throw an exception (fe FileNotFoundException for file handling) and the handling of the IOException/Exception from either the AutoClosable or Closable interface.

Question 11

Given the following code:

class MyResource implement AutoClosable {
public void close() throws IOException { throw new IOException(); }
}

try(MyResource r = new MyResource()) {
throw new IllegalArgumentException();
} catch(Exception e) {
e.printStacktrace();
}

Witch Exception will be catched by the catch?

Answer 11

IllegalArgumentException

When the try-with-resource throws an exception from the close method and the try block also throws an exception. Then the Resource close exception is suppressed.

Question 12

Describe the methods for adding and retrieving suppressed exceptions from a Throwable instance?

Answer 12

public final void addSuppressed(Throwable exception)

public final Throwable[] getSuppressed();

Question 13

Considering the following code:

try {
throw new IOException();
} catch (IOException e | Exception e) {
e.printStackTrace():
}
What is the result?

Answer 13

Compilation failer! Syntax error.

The correct syntax for a multi-catch is:
try {
//
} catch (IOException | SQLException e) {
}

Also when using a multi-catch the declared exceptions can’t be sub-classes or super classes of eachother.

Question 14

Rewrite the following declaration an initzialistation leveraging Diamond operators:
Map> myMap = new HashMap>();

Answer 14

Map> myMap = new HashMap<>();

Question 15

What is the difference between the following:
List l1 = new ArrayList<>();
List l2 = new ArrayList();

Answer 15

l2 is a raw type hashmap, while l1 is of type String using the diamond operator.

Question 16

What is the result of the following:
List l1 = new ArrayList<>();
l1.add(“A”);
l1.addAll(new ArrayList<>());

Answer 16

Compiler error (line 3, addAll)!

You can only use automatic type inference if the target type is clear from the context when creating the object.

Question 17

Considering the following code, what should be added at :

public void myMethod(String ex) throws  {
try {
   if(ex.equals("first")) {
      throw new FirstException();
   } else {
      throw new SecondException();
   }
} catch (Exception e) {
   throw e;
}

Answer 17

Exception
or
FirstException, SecondException

Since Java 7 you can specify more precise throws clauses for rethrows of exceptions.