Oracle 1Z0-851 問題集

質問 1：
Given:
1.public class Plant {
2.private String name;
3.public Plant(String name) { this.name = name; }
4.public String getName() { return name; }
5.}
1.public class Tree extends Plant {
2.public void growFruit() { }
3.public void dropLeaves() { }
4.}
Which statement is true?
A. The code will compile if public Plant() { Plant("fern"); } is added to the Plant class.
B. The code will compile if public Tree() { Plant(); } is added to the Tree class.
C. The code will compile without changes.
D. The code will compile if public Plant() { this("fern"); } is added to the Plant class.
E. The code will compile if public Plant() { Tree(); } is added to the Plant class.
正解：D

質問 2：
Given:
10. interface Jumper { public void jump(); } ...
20. class Animal {} ...
30.class Dog extends Animal {
31.Tail tail; 32. } ...
40.class Beagle extends Dog implements Jumper{
41.public void jump() {}
42.} ...
50.class Cat implements Jumper{
51.public void jump() {}
52.}
Which three are true? (Choose three.)
A. Beagle has-a Tail
B. Beagle has-a Jumper
C. Dog is-a Animal
D. Dog is-a Jumper
E. Cat is-a Jumper
F. Cat has-a Animal
G. Cat is-a Animal
正解：A,C,E

質問 3：
Given:
1.class ClassA {
2.public int numberOfInstances;
3.protected ClassA(int numberOfInstances) {
4.this.numberOfInstances = numberOfInstances;
5.}
6.}
7.public class ExtendedA extends ClassA {
8.private ExtendedA(int numberOfInstances) {
9.super(numberOfInstances);
10.}
11.public static void main(String[] args) {
12.ExtendedA ext = new ExtendedA(420);
13.System.out.print(ext.numberOfInstances);
14.}
15.}
Which statement is true?
A. 420 is the output.
B. An exception is thrown at runtime.
C. Constructors CANNOT use the private modifier.
D. Constructors CANNOT use the protected modifier.
E. All constructors must be declared public.
正解：A

質問 4：
Given:
3.import java.util.*;
4.public class G1 {
5.public void takeList(List<? extends String> list) {
6.// insert code here
7.}
8.}
Which three code fragments, inserted independently at line 6, will compile? (Choose three.)
A. list = new ArrayList<String>();
B. Object o = list;
C. String s = list.get(0);
D. list = new ArrayList<Object>();
E. list.add("foo");
正解：A,B,C

質問 5：
Given:
1.public class Threads2 implements Runnable {
2.3.
public void run() {
4.System.out.println("run.");
5.throw new RuntimeException("Problem");
6.}
7.public static void main(String[] args) {
8.Thread t = new Thread(new Threads2());
9.t.start();
10.System.out.println("End of method.");
11.}
12.}
Which two can be results? (Choose two.)
A. End of method.
java.lang.RuntimeException: Problem
B. java.lang.RuntimeException: Problem
C. run.
java.lang.RuntimeException: Problem
D. run.
java.lang.RuntimeException: Problem
End of method.
E. End of method.
run.
java.lang.RuntimeException: Problem
正解：D,E

質問 6：
Given that the current directory is empty, and that the user has read and write permissions, and the following:
11.import java.io.*;
12.public class DOS {
13.public static void main(String[] args) {
14.File dir = new File("dir");
15.dir.mkdir();
16.File f1 = new File(dir, "f1.txt");
17.try {
18.f1.createNewFile();
19.} catch (IOException e) { ; }
20.File newDir = new File("newDir");
21.dir.renameTo(newDir);
22.}
23.}
Which statement is true?
A. The file system has a directory named dir, containing a file f1.txt.
B. The file system has a new empty directory named newDir.
C. The file system has a new empty directory named dir.
D. Compilation fails.
E. The file system has a directory named newDir, containing a file f1.txt.
正解：E

質問 7：
Given:
11.public class Person {
12.private name;
13.public Person(String name) {
14.this.name = name;
15.}
16.public int hashCode() {
17.return 420;
18.}
19.}
Which statement is true?
A. The time to determine whether a Person object is contained in a HashSet is constant and does NOT depend on the size of the map.
B. The time to find the value from HashMap with a Person key depends on the size of the map.
C. Deleting a Person key from a HashMap will delete all map entries for all keys of type Person.
D. Inserting a second Person object into a HashSet will cause the first Person object to be
removed as a duplicate.
正解：B

質問 8：
Given:
11.public interface A { public void m1(); }
12.13.
class B implements A { }
14.class C implements A { public void m1() { } }
15.class D implements A { public void m1(int x) { } }
16.abstract class E implements A { }
17.abstract class F implements A { public void m1() { } }
18.abstract class G implements A { public void m1(int x) { } } What is the result?
A. Exactly two classes do NOT compile.
B. Compilation succeeds.
C. Exactly one class does NOT compile.
D. Exactly four classes do NOT compile.
E. Exactly three classes do NOT compile.
正解：A