OCA Study Guide 练习回顾

这文章讲OCA准备过程，读过的书籍。 这本书叫 OCA Oracle Certified Associate Java SE 8 Programmer I Study Guide 以下按章节整理错题：

Chapter 1 Java Building Blocks (2/23😄)

18.Which represent the order in which the following statements can be assembled into a program that will compile successfully? (Choose all that apply)
A: class Rabbit {}
B: import java.util.*;
C: package animals;

A. A, B, C
B. B, C, A
C. C, B, A
D. B, A
E. C, A
F. A, C
G. A, B

22.Which of the following are true statements? (Choose all that apply)

A. Java allows operator overloading.
B. Java code compiled on Windows can run on Linux.
C. Java has pointers to specific locations in memory.
D. Java is a procedural language.
E. Java is an object-oriented language.
F. Java is a functional programming language.

Chapter 2 Operators and Statements (3/20😊)

9.How many times will the following code print “Hello World”?

3: for(int i=0; i<10 ; ) {
4: i = i++;
5: System.out.println("Hello World");
6: }

A. 9
B. 10
C. 11
D. The code will not compile because of line 3.
E. The code will not compile because of line 5.
F. The code contains an infinite loop and does not terminate.

16.What is the output of the following code snippet?

3: do {
4: int y = 1;
5: System.out.print(y++ + " ");
6: } while(y <= 10);

A. 1 2 3 4 5 6 7 8 9
B. 1 2 3 4 5 6 7 8 9 10
C. 1 2 3 4 5 6 7 8 9 10 11
D. The code will not compile because of line 6.
E. The code contains an infinite loop and does not terminate.

17.What is the output of the following code snippet?

3:  boolean keepGoing = true;
4:  int result = 15, i = 10;
5:  do {
6:  i--;
7:  if(i==8) keepGoing = false;
8:  result -= 2;
9:  } while(keepGoing);
10: System.out.println(result);

A. 7
B. 9
C. 10
D. 11
E. 15
F. The code will not compile because of line 8.

Chapter 3 Core Java APIs (13/33😂)

4.What is the result of the following code?

7: StringBuilder sb = new StringBuilder();
8: sb.append("aaa").insert(1, "bb").insert(4, "ccc");
9: System.out.println(sb);

A. abbaaccc
B. abbaccca
C. bbaaaccc
D. bbaaccca
E. An exception is thrown.
F. The code does not compile.

5.What is the result of the following code?

2: String s1 = "java";
3: StringBuilder s2 = new StringBuilder("java");
4: if (s1 == s2)
5: System.out.print("1");
6: if (s1.equals(s2))
7: System.out.print("2");

A. 1
B. 2
C. 12
D. No output is printed.
E. An exception is thrown.
F. The code does not compile.

15.Which of these array declarations is not legal? (Choose all that apply)

A. int[][] scores = new int[5][];
B. Object[][][] cubbies = new Object[3][0][5];
C. String beans[] = new beans[6];
D. java.util.Date[] dates[] = new java.util.Date[2][];
E. int[][] types = new int[];
F. int[][] java = new int[][];

16.Which of these compile when replacing line 8? (Choose all that apply)

7: char[]c = new char[2];
8: // INSERT CODE HERE

A. int length = c.capacity;
B. int length = c.capacity();
C. int length = c.length;
D. int length = c.length();
E. int length = c.size;
F. int length = c.size();
G. None of the above.

17.Which of these compile when replacing line 8? (Choose all that apply)

7: ArrayList l = new ArrayList();
8: // INSERT CODE HERE

A. int length = l.capacity;
B. int length = l.capacity();
C. int length = l.length;
D. int length = l.length();
E. int length = l.size;
F. int length = l.size();
G. None of the above.

18.Which of the following are true? (Choose all that apply)

A. An array has a fixed size.
B. An ArrayList has a fixed size.
C. An array allows multiple dimensions.
D. An array is ordered.
E. An ArrayList is ordered.
F. An array is immutable.
G. An ArrayList is immutable.

19.Which of the following are true? (Choose all that apply)

A. Two arrays with the same content are equal.
B. Two ArrayLists with the same content are equal.
C. If you call remove(0) using an empty ArrayList object, it will compile successfully.
D. If you call remove(0) using an empty ArrayList object, it will run successfully.
E. None of the above.

20.What is the result of the following statements?

6:  List<String> list = new ArrayList<String>();
7:  list.add("one");
8:  list.add("two");
9:  list.add(7);
10: for(String s : list) System.out.print(s);

A. onetwo
B. onetwo7
C. onetwo followed by an exception
D. Compiler error on line 9.
E. Compiler error on line 10.

24.What is the result of the following?

6: String [] names = {"Tom", "Dick", "Harry"};
7: List<String> list = names.asList();
8: list.set(0, "Sue");
9: System.out.println(names[0]);

A. Sue
B. Tom
C. Compiler error on line 7.
D. Compiler error on line 8.
E. An exception is thrown.

25.What is the result of the following?

List<String> hex = Arrays.asList("30", "8", "3A", "FF");
Collections.sort(hex);
int x = Collections.binarySearch(hex, "8");
int y = Collections.binarySearch(hex, "3A");
int z = Collections.binarySearch(hex, "4F");
System.out.println(x + " " + y + " " + z);

A. 0 1 –2
B. 0 1 –3
C. 2 1 –2
D. 2 1 –3
E. None of the above.
F. The code doesn’t compile.

26.Which of the following are true statements about the following code? (Choose all that apply)

4: List<Integer> ages = new ArrayList<>();
5: ages.add(Integer.parseInt("5"));
6: ages.add(Integer.valueOf("6"));
7: ages.add(7);
8: ages.add(null);
9: for (int age : ages) System.out.print(age);

A. The code compiles.
B. The code throws a runtime exception.
C. Exactly one of the add statements uses autoboxing.
D. Exactly two of the add statements use autoboxing.
E. Exactly three of the add statements use autoboxing.

29.Which of the following can be inserted into the blank to create a date of June 21, 2014? (Choose all that apply)

import java.time.*;
public class StartOfSummer {
    public static void main(String[] args) {
    LocalDate date = _________
    }
}

A. new LocalDate(2014, 5, 21);
B. new LocalDate(2014, 6, 21);
C. LocalDate.of(2014, 5, 21);
D. LocalDate.of(2014, 6, 21);
E. LocalDate.of(2014, Calendar.JUNE, 21);
F. LocalDate.of(2014, Month.JUNE, 21);

30.What is the output of the following code?

LocalDate date = LocalDate.of(2018, Month.APRIL, 40);
System.out.println(date.getYear() + " " + date.getMonth() + " "
+ date.getDayOfMonth());

A. 2018 APRIL 4
B. 2018 APRIL 30
C. 2018 MAY 10
D. Another date.
E. The code does not compile.
F. A runtime exception is thrown.

Chapter 4 Methods and Encapsulation (14/29😂)

2.Which of the following compile? (Choose all that apply)

A. final static void method4() { }
B. public final int void method() { }
C. private void int method() { }
D. static final void method3() { }
E. void final method() {}
F. void public method() { }

5.Given the following method, which of the method calls return 2? (Choose all that apply)

public int howMany(boolean b, boolean... b2) {
return b2.length;
}

A. howMany();
B. howMany(true);
C. howMany(true, true);
D. howMany(true, true, true);
E. howMany(true, {true});
F. howMany(true, {true, true});
G. howMany(true, new boolean[2]);

6.Which of the following are true? (Choose all that apply)

A. Package private access is more lenient than protected access.
B. A public class that has private fields and package private methods is not visible to classes outside the package.
C. You can use access modifiers so only some of the classes in a package see a particular package private class.
D. You can use access modifiers to allow read access to all methods, but not any instance variables.
E. You can use access modifiers to restrict read access to all classes that begin with the word Test.

9.Which are methods using JavaBeans naming conventions for accessors and mutators? (Choose all that apply)

A. public boolean getCanSwim() { return canSwim;}
B. public boolean canSwim() { return numberWings;}
C. public int getNumWings() { return numberWings;}
D. public int numWings() { return numberWings;}
E. public void setCanSwim(boolean b) { canSwim = b;}

11.Which are true of the following code? (Choose all that apply)

1:  public class Rope {
2:    public static void swing() {
3:        System.out.print("swing ");
4:    }
5:    public void climb() {
6:        System.out.println("climb ");
7:    }
8:    public static void play() {
9:        swing();
10:       climb();
11:   }
12:   public static void main(String[] args) {
13:       Rope rope = new Rope();
14:       rope.play();
15:       Rope rope2 = null;
16:       rope2.play();
17:   }
18: }

A. The code compiles as is.
B. There is exactly one compiler error in the code.
C. There are exactly two compiler errors in the code.
D. If the lines with compiler errors are removed, the output is climb climb .
E. If the lines with compiler errors are removed, the output is swing swing .
F. If the lines with compile errors are removed, the code throws a NullPointerException.

12.What is the output of the following code?

import rope.*;
import static rope.Rope.*;
public class RopeSwing {
    private static Rope rope1 = new Rope();
    private static Rope rope2 = new Rope();
    {
        System.out.println(rope1.length);
    }
    public static void main(String[] args) {
        rope1.length = 2;
        rope2.length = 8;
        System.out.println(rope1.length);
    }
}
package rope;
public class Rope {
    public static int length = 0;
}

A. 02
B. 08
C. 2
D. 8
E. The code does not compile.
F. An exception is thrown.

15.What is the result of the following statements?

1:  public class Test {
2:    public void print(byte x) {
3:      System.out.print("byte");
4:    }
5:    public void print(int x) {
6:      System.out.print("int");
7:    }
8:    public void print(float x) {
9:      System.out.print("float");
10:   }
11:   public void print(Object x) {
12:     System.out.print("Object");
13:   }
14:   public static void main(String[] args) {
15:     Test t = new Test();
16:     short s = 123;
17:     t.print(s);
18:     t.print(true);
19:     t.print(6.789);
20:   }
21: }

A. bytefloatObject
B. intfloatObject
C. byteObjectfloat
D. intObjectfloat
E. intObjectObject
F. byteObjectObject

17.Which of the following are output by the following code? (Choose all that apply)

public class StringBuilders {
    public static StringBuilder work(StringBuilder a,
    StringBuilder b) {
        a = new StringBuilder("a");
        b.append("b");
        return a;
    }
    public static void main(String[] args) {
        StringBuilder s1 = new StringBuilder("s1");
        StringBuilder s2 = new StringBuilder("s2");
        StringBuilder s3 = work(s1, s2);
        System.out.println("s1 = " + s1);
        System.out.println("s2 = " + s2);
        System.out.println("s3 = " + s3);
    }
}

A. s1 = a
B. s1 = s1
C. s2 = s2
D. s2 = s2b
E. s3 = a
F. s3 = null
G. The code does not compile.

18.Which of the following are true? (Choose 2)

A. this() can be called from anywhere in a constructor.
B. this() can be called from any instance method in the class.
C. this.variableName can be called from any instance method in the class.
D. this.variableName can be called from any static method in the class.
E. You must include a default constructor in the code if the compiler does not include one.
F. You can call the default constructor written by the compiler using this().
G. You can access a private constructor with the main() method.

20.Which code can be inserted to have the code print 2?

public class BirdSeed {
    private int numberBags;
    boolean call;

    public BirdSeed() {
        // LINE 1
        call = false;
        // LINE 2
    }
    public BirdSeed(int numberBags) {
        this.numberBags = numberBags;
    }
    public static void main(String[] args) {
        BirdSeed seed = new BirdSeed();
        System.out.println(seed.numberBags);
} }

A. Replace line 1 with BirdSeed(2);
B. Replace line 2 with BirdSeed(2);
C. Replace line 1 with new BirdSeed(2);
D. Replace line 2 with new BirdSeed(2);
E. Replace line 1 with this(2);
F. Replace line 2 with this(2);

22.What is the result of the following?

1: public class Order {
2:   static String result = "";
3:   { result += "c"; }
4:   static
5:   { result += "u"; }
6:   { result += "r"; }
7: }

1: public class OrderDriver {
2:   public static void main(String[] args) {
3:     System.out.print(Order.result + " ");
4:     System.out.print(Order.result + " ");
5:     new Order();
6:     new Order();
7:     System.out.print(Order.result + " ");
8:   }
9: }

A. curur
B. ucrcr
C. u ucrcr
D. u u curcur
E. u u ucrcr
F. ur ur urc
G. The code does not compile.

26.What is the result of the following class?

1: import java.util.function.*;
2: 
3: public class Panda {
4:   int age;
5:   public static void main(String[] args) {
6:     Panda p1 = new Panda();
7:     p1.age = 1;
8:     check(p1, p -> p.age < 5);
9:   }
10:  private static void check(Panda panda, Predicate<Panda> pred) {
11:    String result = pred.test(panda) ? "match" : "not match";
12:    System.out.print(result);
13: } }

A. match
B. not match
C. Compiler error on line 8.
D. Compiler error on line 10.
E. Compiler error on line 11.
F. A runtime excep

27.What is the result of the following code?

1:  interface Climb {
2:    boolean isTooHigh(int height, int limit);
3:  }
4:  
5:  public class Climber {
6:    public static void main(String[] args) {
7:      check((h, l) -> h.append(l).isEmpty(), 5);
8:    }
9:    private static void check(Climb climb, int height) {
10:     if (climb.isTooHigh(height, 10))
11:       System.out.println("too high");
12:     else
13:       System.out.println("ok");
14:   }
15: }

A. ok
B. too high
C. Compiler error on line 7.
D. Compiler error on line 10.
E. Compiler error on a different line.
F. A runtime exception is thrown.

29.Which lambda can replace the MySecret class to return the same value? (Choose all that apply)

interface Secret {
  String magic(double d);
}
class MySecret implements Secret {
  public String magic(double d) {
    return "Poof";
  }
}

A. caller((e) -> "Poof");
B. caller((e) -> {"Poof"});
C. caller((e) -> { String e = ""; "Poof" });
D. caller((e) -> { String e = ""; return "Poof"; });
E. caller((e) -> { String e = ""; return "Poof" });
F. caller((e) -> { String f = ""; return "Poof"; });

Chapter 5 Class Design (12/20😭)

1.What modifiers are implicitly applied to all interface methods? (Choose all that apply)

A. protected
B. public
C. static
D. void
E. abstract
F. default

2.What is the output of the following code?

1:  class Mammal {
2:    public Mammal(int age) {
3:      System.out.print("Mammal");
4:    }
5:  }
6:  public class Platypus extends Mammal {
7:    public Platypus() {
8:      System.out.print("Platypus");
9:    }
10:   public static void main(String[] args) {
11:     new Mammal(5);
12:   }
13: }

A. Platypus
B. Mammal
C. PlatypusMammal
D. MammalPlatypus
E. The code will not compile because of line 7.
F. The code will not compile because of line 11.

3.Which of the following statements can be inserted in the blank line so that the code will compile successfully? (Choose all that apply)

public interface CanHop {}
public class Frog implements CanHop {
  public static void main(String[] args) {
    ____________frog = new TurtleFrog();
  }
}
public class BrazilianHornedFrog extends Frog {}
public class TurtleFrog extends Frog {}

A. Frog
B. TurtleFrog
C. BrazilianHornedFrog
D. CanHop
E. Object
F. Long

4.Which statement(s) are correct about the following code? (Choose all that apply)

public class Rodent {
  protected static Integer chew() throws Exception {
    System.out.println("Rodent is chewing");
    return 1;
  }
}
public class Beaver extends Rodent {
  public Number chew() throws RuntimeException {
    System.out.println("Beaver is chewing on wood");
    return 2;
  }
}

A. It will compile without issue.
B. It fails to compile because the type of the exception the method throws is a subclass of the type of exception the parent method throws.
C. It fails to compile because the return types are not covariant.
D. It fails to compile because the method is protected in the parent class and public in the subclass.
E. It fails to compile because of a static modifier mismatch between the two methods.

5.Which of the following may only be hidden and not overridden? (Choose all that apply)

A. private instance methods
B. protected instance methods
C. public instance methods
D. static methods
E. public variables
F. private variables

8.Choose the correct statement about the following code:

1: public interface Herbivore {
2:   int amount = 10;
3:   public static void eatGrass();
4:   public int chew() {
5:     return 13;
6:   }
7: }

A. It compiles and runs without issue.
B. The code will not compile because of line 2.
C. The code will not compile because of line 3.
D. The code will not compile because of line 4.
E. The code will not compile because of lines 2 and 3.
F. The code will not compile because of lines 3 and 4.

10.Which statements are true for both abstract classes and interfaces? (Choose all that apply)

A. All methods within them are assumed to be abstract.
B. Both can contain public static final variables.
C. Both can be extended using the extends keyword.
D. Both can contain default methods.
E. Both can contain static methods.
F. Neither can be instantiated directly.
G. Both inherit java.lang.Object.

11.What modifiers are assumed for all interface variables? (Choose all that apply)

A. public
B. protected
C. private
D. static
E. final
F. abstract

16.What is the output of the following code?

1:  abstract class Reptile {
2:    public final void layEggs() { System.out.println("Reptile laying eggs"); }
3:    public static void main(String[] args) {
4:      Reptile reptile = new Lizard();
5:      reptile.layEggs();
6:    }
7:  }
8:  public class Lizard extends Reptile {
9:    public void layEggs() { System.out.println("Lizard laying eggs"); }
10: }

A. Reptile laying eggs
B. Lizard laying eggs
C. The code will not compile because of line 4.
D. The code will not compile because of line 5.
E. The code will not compile because of line 9.

18.What is the output of the following code? (Choose all that apply)

1:  interface Aquatic {
2:    public default int getNumberOfGills(int input) { return 2; }
3:  }
4:  public class ClownFish implements Aquatic {
5:    public String getNumberOfGills() { return "4"; }
6:    public String getNumberOfGills(int input) { return "6"; }
7:    public static void main(String[] args) {
8:      System.out.println(new ClownFish().getNumberOfGills(-1));
9:    }
10: }

A. 2
B. 4
C. 6
D. The code will not compile because of line 5.
E. The code will not compile because of line 6.
F. The code will not compile because of line 8.

19.Which of the following statements can be inserted in the blank so that the code will compile successfully? (Choose all that apply)

public class Snake {}
public class Cobra extends Snake {}
public class GardenSnake {}
public class SnakeHandler {
  private Snake snake;
  public void setSnake(Snake snake) { this.snake = snake; }
  public static void main(String[] args) {
    new SnakeHandler().setSnake(__________);
  }
}

A. new Cobra()
B. new GardenSnake()
C. new Snake()
D. new Object()
E. new String("Snake")
F. null

20.What is the result of the following code?

1:  public abstract class Bird {
2:    private void fly() { System.out.println("Bird is flying"); }
3:    public static void main(String[] args) {
4:      Bird bird = new Pelican();
5:      bird.fly();
6:    }
7:  }
8:  class Pelican extends Bird {
9:    protected void fly() { System.out.println("Pelican is flying"); }
10: }

A. Bird is flying
B. Pelican is flying
C. The code will not compile because of line 4.
D. The code will not compile because of line 5.
E. The code will not compile because of line 9.

Chapter 6 Exceptions (12/20😭)

1.Which of the following statements are true? (Choose all that apply)

A. Runtime exceptions are the same thing as checked exceptions.
B. Runtime exceptions are the same thing as unchecked exceptions.
C. You can declare only checked exceptions.
D. You can declare only unchecked exceptions.
E. You can handle only Exception subclasses.

2.Which of the following pairs fill in the blanks to make this code compile? (Choose all that apply)

7: public void ohNo() _____ Exception {
8: _____________ Exception();
9: }

A. On line 7, fill in throw
B. On line 7, fill in throws
C. On line 8, fill in throw
D. On line 8, fill in throw new
E. On line 8, fill in throws
F. On line 8, fill in throws new

5.Which of the following exceptions are thrown by the JVM? (Choose all that apply)

A. ArrayIndexOutOfBoundsException
B. ExceptionInInitializerError
C. java.io.IOException
D. NullPointerException
E. NumberFormatException

7.What is printed besides the stack trace caused by the NullPointerException from line 16?

1:  public class DoSomething {
2:    public void go() {
3:      System.out.print("A");
4:      try {
5:        stop();
6:      } catch (ArithmeticException e) {
7:        System.out.print("B");
8:      } finally {
9:        System.out.print("C");
10:     }
11:     System.out.print("D");
12:   }
13:   public void stop() {
14:     System.out.print("E");
15:     Object x = null;
16:     x.toString();
17:     System.out.print("F");
18:   }
19:   public static void main(String[] args) {
20:     new DoSomething().go();
21:   }
22: }

A. AE
B. AEBCD
C. AEC
D. AECD
E. No output appears other than the stack trace.

13.Which of the following statements are true? (Choose all that apply)

A. You can declare a method with Exception as the return type.
B. You can declare any subclass of Error in the throws part of a method declaration.
C. You can declare any subclass of Exception in the throws part of a method declaration.
D. You can declare any subclass of Object in the throws part of a method declaration.
E. You can declare any subclass of RuntimeException in the throws part of a method declaration.

14.Which of the following can be inserted on line 8 to make this code compile? (Choose all that apply)

7: public void ohNo() throws IOException {
8:   // INSERT CODE HERE
9: }

A. System.out.println("it's ok");
B. throw new Exception();
C. throw new IllegalArgumentException();
D. throw new java.io.IOException();
E. throw new RuntimeException();

15.Which of the following are unchecked exceptions? (Choose all that apply)

A. ArrayIndexOutOfBoundsException
B. IllegalArgumentException
C. IOException
D. NumberFormatException
E. Any exception that extends RuntimeException
F. Any exception that extends Exception

16.Which scenario is the best use of an exception?

A. An element is not found when searching a list.
B. An unexpected parameter is passed into a method.
C. The computer caught fire.
D. You want to loop through a list.
E. You don’t know how to code a method.

17.Which of the following can be inserted into Lion to make this code compile? (Choose all that apply)

class HasSoreThroatException extends Exception {}
class TiredException extends RuntimeException {}
interface Roar {
  void roar() throws HasSoreThroatException;
}
class Lion implements Roar {// INSERT CODE HERE
}

A. public void roar(){}
B. public void roar() throws Exception{}
C. public void roar() throws HasSoreThroatException{}
D. public void roar() throws IllegalArgumentException{}
E. public void roar() throws TiredException{}

18.Which of the following are true? (Choose all that apply)

A. Checked exceptions are allowed to be handled or declared.
B. Checked exceptions are required to be handled or declared.
C. Errors are allowed to be handled or declared.
D. Errors are required to be handled or declared.
E. Runtime exceptions are allowed to be handled or declared.
F. Runtime exceptions are required to be handled or declared.

19.Which of the following can be inserted in the blank to make the code compile? (Choose all that apply)

public static void main(String[] args) {
  try {
    System.out.println("work real hard");
  } catch ( ______ e) {
  } catch (RuntimeException e) {
  }
}

A. Exception
B. IOException
C. IllegalArgumentException
D. RuntimeException
E. StackOverflowError
F. None of the above.

20.What does the output of the following contain? (Choose all that apply)

12: public static void main(String[] args) {
13:   System.out.print("a");
14:   try {
15:     System.out.print("b");
16:     throw new IllegalArgumentException();
17:   } catch (IllegalArgumentException e) {
18:     System.out.print("c");
19:     throw new RuntimeException("1");
20:   } catch (RuntimeException e) {
21:     System.out.print("d");
22:     throw new RuntimeException("2");
23:   } finally {
24:     System.out.print("e");
25:     throw new RuntimeException("3");
26:   }
27: }

A. abce
B. abde
C. An exception with the message set to “1”
D. An exception with the message set to “2”
E. An exception with the message set to “3”
F. Nothing, the code does not compile.