SCJP刷题学习笔记（Part six）

QUESTION 51

Given:

final class Folder { //line n1
//line n2
public void open () {
System.out.print(“Open”);
}
}

public class Test {
public static void main (String [] args) throws Exception {
try (Folder f = new Folder()) {
f.open();
}
}
}

Which two modifications enable the code to print Open Close? (Choose two.)

A. Replace line n1 with:

class Folder implements AutoCloseable {

B. Replace line n1 with:

class Folder extends Closeable {

C. Replace line n1 with:

class Folder extends Exception {

D. At line n2, insert:

final void close () {

System.out.print(“Close”);

}

E. At line n2, insert:

public void close () throws IOException {

System.out.print(“Close”);

}

Correct Answer: AE

Section: (none)

Explanation

Explanation/Reference:

Partthree涉及到的AutoCloseable,Closeable和Flushable接口:

https://blog.csdn.net/weixin_30656145/article/details/98637024

QUESTION 52

You want to create a singleton class by using the Singleton design pattern.

Which two statements enforce the singleton nature of the design? (Choose two.)

A. Make the class static.

B. Make the constructor private.

C. Override equals() and hashCode() methods of the java.lang.Object class.

D. Use a static reference to point to the single instance.

E. Implement the Serializable interface.

Correct Answer: BD

Section: (none)

Explanation

Explanation/Reference:

QUESTION 53

Given the code fragment:

9. Connection conn = DriveManager.getConnection(dbURL, userName, passWord);
10. String query = “SELECT id FROM Employee”;
11. try (Statement stmt = conn.createStatement()) {
12. ResultSet rs = stmt.executeQuery(query);
13. stmt.executeQuery(“SELECT id FROM Customer”);
14. while (rs.next()) {
15. //process the results
16. System.out.println(“Employee ID: “+ rs.getInt(“id”));
17. }
18. } catch (Exception e) {
19. System.out.println (“Error”);
20. }

Assume that:

The required database driver is configured in the classpath.

The appropriate database is accessible with the dbURL, userName, and passWord exists.

The Employee and Customer tables are available and each table has id column with a few records and

the SQL queries are valid.

What is the result of compiling and executing this code fragment?

A. The program prints employee IDs.

B. The program prints customer IDs.

C. The program prints Error.

D. compilation fails on line 13.

Correct Answer: C

Section: (none)

Explanation

Explanation/Reference:

QUESTION 54

Given the code fragment:

List<Integer> codes = Arrays.asList (10, 20);
UnaryOperator<Double> uo = s -> s +10.0;
codes.replaceAll(uo);
codes.forEach(c -> System.out.println(c));

What is the result?

A. 20.0

30.0

B. 10

C. A compilation error occurs.

D. A NumberFormatException is thrown at run time.

Correct Answer: C

Section: (none)

Explanation

Syntax error on token "Invalid Character", delete this token

Explanation/Reference:Part one 涉及到的UnaryOperator说明：

https://blog.csdn.net/qq_28410283/article/details/80634319

QUESTION 55

Given:

public class Customer {
private String fName;
private String lName;
private static int count;
public Customer (String first, String last) {fName = first; lName = last;
++count;}
static { count = 0; }
public static int getCount() {return count; }
}

public class App {
public static void main (String [] args) {
Customer c1 = new Customer(“Larry”, “Smith”);
Customer c2 = new Customer(“Pedro”, “Gonzales”);
Customer c3 = new Customer(“Penny”, “Jones”);
Customer c4 = new Customer(“Lars”, “Svenson”);
c4 = null;
c3 = c2;
System.out.println (Customer.getCount());
}
}

What is the result?

A. 0

B. 2

C. 3

D. 4

E. 5

Correct Answer: D

Section: (none)

Explanation

Explanation/Reference:

重载与重写的区别：https://blog.csdn.net/linzhaojie525/article/details/55213010

QUESTION 56

Given:

Item table
• ID, INTEGER: PK
• DESCRIP, VARCHAR(100)
• PRICE, REAL
• QUANTITY< INTEGER

And given the code fragment:

9. try {
10. Connection conn = DriveManager.getConnection(dbURL, username, password);
11. String query = “Select * FROM Item WHERE ID = 110”;
12. Statement stmt = conn.createStatement();
13. ResultSet rs = stmt.executeQuery(query);
14. while(rs.next()) {
15. System.out.println(“ID: “ + rs.getInt(“Id”));
16. System.out.println(“Description: “ + rs.getString(“Descrip”));
17. System.out.println(“Price: “ + rs.getDouble(“Price”));
18. System.out.println(Quantity: “ + rs.getInt(“Quantity”));
19. }
20. } catch (SQLException se) {
21. System.out.println(“Error”);
22. }

Assume that:

The required database driver is configured in the classpath.

The appropriate database is accessible with the dbURL, userName, and passWord exists.

The SQL query is valid.

What is the result?

A. An exception is thrown at runtime.

B. Compilation fails.

C. The code prints Error.

D. The code prints information about Item 110.

Correct Answer: D

Section: (none)

Explanation

Explanation/Reference:

QUESTION 57

Given:

class Worker extends Thread {
CyclicBarrier cb;
public Worker(CyclicBarrier cb) { this.cb = cb; }
public void run () {
try {
cb.await();
System.out.println(“Worker…”);
} catch (Exception ex) { }
}
}
class Master implements Runnable { //line n1
public void run () {
System.out.println(“Master…”);
}
}

and the code fragment:

Master master = new Master();
//line n2
Worker worker = new Worker(cb);
worker.start();

You have been asked to ensure that the run methods of both the Worker and Master classes are

executed.

Which modification meets the requirement?

A. At line n2, insert CyclicBarrier cb = new CyclicBarrier(2, master);

B. Replace line n1 with class Master extends Thread {

C. At line n2, insert CyclicBarrier cb = new CyclicBarrier(1, master);

D. At line n2, insert CyclicBarrier cb = new CyclicBarrier(master);

Correct Answer: C

Section: (none)

Explanation

Explanation/Reference:

CyclicBarrier(栅栏)使用详解：https://blog.csdn.net/J080624/article/details/85261930

QUESTION 58

Given the code fragment:

String str = “Java is a programming language”;
ToIntFunction<String> indexVal = str: : indexOf; //line n1
int x = indexVal.applyAsInt(“Java”); //line n2
System.out.println(x);

What is the result?

A. 0

B. 1

C. A compilation error occurs at line n1.

D. A compilation error occurs at line n2.

Correct Answer: A

Section: (none)

Explanation

Explanation/Reference:

常用lamdba函数式接口：https://blog.csdn.net/Mr_PH/article/details/82424607

QUESTION 59

Given the code fragment:

List<String> codes = Arrays.asList (“DOC”, “MPEG”, “JPEG”);
codes.forEach (c -> System.out.print(c + “ “));
String fmt = codes.stream()
.filter (s-> s.contains (“PEG”))
.reduce((s, t) -> s + t).get();
System.out.println(“\n” + fmt);

What is the result?

A. DOC MPEG JPEG

MPEGJPEG

B. DOC MPEG MPEGJPEG

MPEGMPEGJPEG

C. MPEGJPEG

MPEGJPEG

D. The order of the output is unpredictable.

Correct Answer: A

Section: (none)

Explanation

Explanation/Reference:

Part two 涉及到的Stream语法：https://blog.csdn.net/SeanTandol/article/details/86630437

QUESTION 60

Given the code fragment:

    List<String> nL = Arrays.asList("Jim", "John", "Jeff");Function<String, String> funVal = s -> "Hello : ".concat(s);nL.stream().map(funVal).peek(System.out::print);

What is the result?

A. Hello : Jim Hello : John Hello : Jeff

B. Jim John Jeff

C. The program prints nothing.

D. A compilation error occurs.

Correct Answer: C

Section: (none)

Explanation

Explanation/Reference:

Part one 涉及到的Function拓展说明：https://blog.csdn.net/justry_deng/article/details/100886475
Part two 涉及到的Stream语法：https://blog.csdn.net/SeanTandol/article/details/86630437

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