1Z0-809: Java SE 8 Programmer II Certification Exam Practice Exam

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1Z0-809: Java SE 8 Programmer II Certification Exam Practice Exam

Given these code fragments:

class MyThread implements Runnable \{  
    private static AtomicInteger count = new AtomicInteger(0);  
  
    public void run() \{  
        int x = count.incrementAndGet();  
        System.out.print(x + " ");  
    \}  
\}

Thread thread1 = new Thread(new MyThread());  
Thread thread2 = new Thread(new MyThread());  
Thread thread3 = new Thread(new MyThread());  
Thread[] ta = \{thread1, thread2, thread3\};  
  
for (int x = 0; x &lt; 3; x++) \{  
    ta[x].start();  
\}

Which statement is correct?

A The program prints 1 2 3 and the order is unpredictable.
B The program prints 1 2 3.
C The program prints 1 1 1.
D A compilation error occurs.

Explanation

A static AtomicInteger is shared by every MyThread instance. Its incrementAndGet() operation is atomic, so the three invocations obtain the unique values 1, 2, and 3. Scheduling is nondeterministic, so the print order is unpredictable.

Given the following declarations:

public class Canvas implements Drawable \{  
    public void draw() \{ \}  
\}  
  
public abstract class Board extends Canvas \{ \}  
  
public class Paper extends Canvas \{  
    protected void draw(int color) \{ \}  
\}  
  
public class Frame extends Canvas implements Drawable \{  
    public void resize() \{ \}  
\}  
  
public interface Drawable \{  
    public abstract void draw();  
\}

Which statement is correct?

A Board does not compile.
B Paper does not compile.
C Frame does not compile.
D Drawable does not compile.
E All classes compile successfully.

Explanation

All classes compile successfully. Canvas provides the required public draw() implementation. Board, Paper, and Frame inherit that implementation; Paper.draw(int) is a valid overload rather than an invalid reduction of visibility, and Frame may redundantly declare that it implements Drawable.

Given this code fragment:

class CallerThread implements Callable&lt;String&gt; \{  
    String str;  
    public CallerThread(String s) \{ this.str = s; \}  
    public String call() throws Exception \{  
        return str.concat("Call");  
    \}  
\}

and

public static void main(String[] args) throws InterruptedException, ExecutionException \{  
    ExecutorService es = Executors.newFixedThreadPool(4); // line n1  
    Future f1 = es.submit(new CallerThread("Call"));  
    String str = f1.get().toString();  
    System.out.println(str);  
\}

Which statement is correct?

A The program prints Call Call and terminates.
B The program prints Call Call and does not terminate.
C A compilation error occurs at line n1.
D An ExecutionException is thrown at run time.

Explanation

The Callable returns "CallCall", and Future.get() retrieves that successful result for printing. Because the fixed-thread-pool ExecutorService is never shut down, it is not terminated after the task completes; an orderly shutdown requires calling shutdown() (and, if needed, waiting with awaitTermination). Java ExecutorService documentation

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Java SE 21 ExecutorService API

Given this code fragment:

public class Foo \{  
    public static void main(String[] args) \{  
        Map&lt;Integer, String&gt; unsortMap = new HashMap&lt;&gt;();  
        unsortMap.put(10, "z");  
        unsortMap.put(5, "b");  
        unsortMap.put(1, "d");  
        unsortMap.put(7, "e");  
        unsortMap.put(50, "j");  
        Map&lt;Integer, String&gt; treeMap = new TreeMap&lt;Integer, String&gt;(new  
        Comparator&lt;Integer&gt;() \{  
            @Override public int compare(Integer o1, Integer o2) \{ return o2.compareTo  
            (o2); \}  
        \});  
        treeMap.putAll(unsortMap);  
        for (Map.Entry&lt;Integer, String&gt; entry : treeMap.entrySet()) \{  
            System.out.print(entry.getValue() + " ");  
        \}  
    \}  
\}

What is the result?

A A compilation error occurs.
B d b e z j
C j z e b d
D z b d e j

Explanation

The source as shown does not import the java.util types used by Map, HashMap, TreeMap, Comparator, and Map.Entry; those unresolved types cause compilation to fail.

Given the following class:

class Book \{  
    int id;  
    String name;  
  
    public Book(int id, String name) \{  
        this.id = id;  
        this.name = name;  
    \}  
  
    public boolean equals(Object obj) \{ // line n1  
        boolean output = false;  
        Book b = (Book) obj;  
        if (this.id == b.id) \{  
            output = true;  
        \}  
        return output;  
    \}  
\}

And this code fragment:

Book b1 = new Book(101, "Java Programing");  
Book b2 = new Book(102, "Java Programing");  
System.out.println(b1.equals(b2)); // line n2

Which statement is correct?

A The program prints true.
B The program prints false.
C A compilation error occurs. To ensure successful compilation, replace line n1 with: boolean equals (Book obj) {
D A compilation error occurs. To ensure successful compilation, replace line n2 with: System.out.println (b1.equals((Object) b2));

Explanation

equals(Object) is a valid method signature. It compares the id fields of the two Book objects, and 101 == 102 evaluates to false; therefore, the printed value is false.

Given this code fragment:

public static void main (String [ ] args) throws IOException \{  
BufferedReader br = new BufferedReader (new InputStremReader (System.in));  
System.out.print ("Enter GDP: ");  
//line 1  
\}

Which code fragment, inserted at line 1, allows the code to read the GDP entered by the user?

A int GDP = Integer.parseInt (br.readline());
B int GDP = br.read();
C int GDP = br.nextInt();
D int GDP = Integer.parseInt (br.next());

Explanation

BufferedReader.read() reads the next input character and returns its value as an int, so its result can be stored in an int variable. BufferedReader does not provide nextInt() or next(), and its line-reading method is named readLine(), not readline().

Given this code fragment:

BiFunction&lt;Integer, Double, Integer&gt; val = (t1, t2) -&gt; t1 + t2; // line n1  
System.out.println(val.apply(10, 10.5));

What is the result?

A 20
B 20.5
C A compilation error occurs at line n1.
D A compilation error occurs at line n2.

Explanation

Adding an Integer and a Double unboxes both operands and yields a double. The BiFunction declares Integer as its result type, and Java does not implicitly narrow a double result to int and box it into an Integer; therefore, the lambda fails to compile at line n1.

Given this code fragment:

List&lt;Integer&gt; values = Arrays.asList (1, 2, 3);  
values.stream ()  
.map(n -&gt; n*2) //line n1  
.peek(System.out::print) //line n2  
.count();

What is the result?

A 246
B The code produces no output.
C A compilation error occurs at line n1.
D A compilation error occurs at line n2.

Explanation

count() may use the stream’s known size rather than traverse its elements. The Stream API permits eliding intermediate operations when doing so does not affect the terminal result; therefore the peek action is not guaranteed to run, and nothing is printed.

Given this code fragment:

ZonedDateTime depart = ZonedDateTime.of(2015, 1, 15, 3, 0, 0, 0, ZoneID.of("UTC-7"));  
ZonedDateTime arrive = ZonedDateTime.of(2015, 1, 15, 9, 0, 0, 0, ZoneID.of("UTC-5")); long hrs = ChronoUnit.HOURS.between(depart, arrive); //line n1  
System.out.println("Travel time is" + hrs + "hours");

What is the outcome?

A Travel time is 4 hours
B Travel time is 6 hours
C Travel time is 8 hours
D An exception is thrown at line n1.

Explanation

Time-based units for ZonedDateTime operate on the instant timeline. 03:00 at UTC−7 corresponds to 10:00 UTC, while 09:00 at UTC−5 corresponds to 14:00 UTC, producing an elapsed interval of four hours.

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ZonedDateTime (Java SE 8 API)

Given the records in the Player table:

Question Image

and the following code fragment:

try \{  
Connection conn = DriverManager.getConnection(URL, username, password);  
Statement st= conn.createStatement(  
ResultSet.TYPE_SCROLL_SENSITIVE,  
ResultSet.CONCUR_UPDATABLE);  
st.execute ("SELECT * FROM Player");  
st.setMaxRows(2);  
ResultSet rs = st.getResultSet();  
rs.absolute(3);  
while (rs.next ()) \{  
System.out.println(rs.getInt(1) + " " + rs.getString(2));  
\}  
\} catch (SQLException ex) \{  
System.out.print("SQLException is thrown.");  
\}

Assume that:

The required database driver is configured in the classpath.
The appropriate database is accessible with URL, username, and password.
The SQL query is valid.

What is the output?

A 2 Jack 3 Sam
B The program prints nothing.
C 3 Sam
D SQLException is thrown.

Explanation

ResultSet.absolute(3) places the cursor on row 3. ResultSet.next() advances it one row; because there is no row after the third row, it returns false, so the loop body does not execute and nothing is printed. The Java ResultSet API specifies these cursor movements.

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Java ResultSet API

Given this code fragment:

Path p1 = Paths.get("/Pics/MyPic.jpeg");  
System.out.println(p1.getNameCount() +  
    ":" + p1.getName(1) +  
    ":" + p1.getFileName());

Assume that the Pics directory does not exist. What is the result?

A An exception is thrown at run time.
B 2:MyPic.jpeg: MyPic.jpeg
C 3:.:MyPic.jpeg
D 2:Pics: MyPic.jpeg

Explanation

A Path is a lexical representation and its component-access methods do not access the file system. The root is not a name element, so /Pics/MyPic.jpeg has two name elements. Index 1 and the file name are both MyPic.jpeg; the directory’s nonexistence does not cause an exception. Oracle specifies that getNameCount() returns name elements, getName(0) is nearest the root, and getFileName() returns the farthest name element from the root.

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Java Path API

Given the following Product class:

public class Product \{  
    int id;  
    int price;  
  
    public Product(int id, int price) \{  
        this.id = id;  
        this.price = price;  
    \}  
  
    Public String toString() \{ return id + ":" + price;)  
\}

And this code fragment:

List&lt;Product&gt; products = new ArrayList&lt;&gt;(Arrays.asList(  
    new Product(1, 10), new Product(2, 30), new Product(3, 20)  
));  
Product p = products.stream().reduce(new Product(4, 0), (p1, p2) -&gt; \{  
    p1.price += p2.price;  
    return new Product(p1.id, p1.price);  
\});  
products.add(p);  
products.stream().parallel()  
    .reduce((p1, p2) -&gt; p1.price &gt; p2.price ? p1 : p2)  
    .ifPresent(System.out::println);

What is the result?

A 4:60
B 2:30
C 4:60 2:30 3:20 1:10
D 4:0
E The program prints nothing

Explanation

The first reduction accumulates the three prices into the identity product, yielding a product with id 4 and price 60. After that product is added to the list, the parallel reduction selects the product with the largest price, so it prints 4:60.

Given this code fragment:

List&lt;String&gt; colors = Arrays.asList("red", "green", "yellow");  
Predicate&lt;String&gt; test = n - &gt; \{  
System.out.println("Searching"¦");  
return n.contains("red");  
\};  
colors.stream()  
.filter(c -&gt; c.length() &gt; 3)  
.allMatch(test);

What is the outcome?

A Searching...
B Searching... Searching...
C Searching... Searching... Searching...
D A compilation error occurs.

Explanation

A Java lambda expression requires the -> token between its parameter list and body. Writing n - > separates that required token into the minus and greater-than operators, so the predicate declaration is invalid and compilation fails.

Learn more

Java Language Specification, §15.27 Lambda Expressions