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Quiz by , created over 3 years ago

Nietrywialne pytania napotkane podczas nauki do OCAJP7. Może służyć do przypominania sobie mechanizmów języka.

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Object Oriented Programming Concepts
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Macbeth Quotes To Learn
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Java Practice 1
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Java Core. Basics
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Java Practice 2
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Programming Review
Shannon Anderson-Rush

Question 1

Question
Which of the following is illegal:
Answer
  • int i = 32;
  • float f = 45.0;
  • double d = 45.0;

Question 2

Question
public class Test { static int age; public static void main (String args []) { age = age + 1; System.out.println("The age is " + age); } }
Answer
  • Compiles and runs with no output
  • Compiles and runs printing out The age is 1
  • Compiles but generates a runtime error
  • Does not compile
  • Compiles but generates a compile time error

Question 3

Question
public static void main(String[] args) { int age; System.out.println(age+1); }
Answer
  • Compiles and runs with no output
  • Compiles and runs printing out The age is 1
  • Compiles but generates a runtime error
  • Does not compile
  • Compiles but generates a compile time error

Question 4

Question
Which of the following return true?
Answer
  • "john" == "john"
  • "john".equals("john")
  • "john" = "john"
  • "john".equals(new Button("john"))

Question 5

Question
Which of the following is correct:
Answer
  • String temp [] = new String {"j", "a", "z"};
  • String temp [] = {"a", "b", "c"};
  • String temp = {"a", "b", "c"};
  • String temp [] = new String [] {"j" "a" "z"};
  • String temp [] = new String[3] {"j" "a" "z"};

Question 6

Question
Compiler adds default constructor to class which hasn't got constructor with empty argument list. Is it true?
Answer
  • True
  • False

Question 7

Question
Which of the following are acceptable to the Java 7 compiler?
Answer
  • if (2 == 3) System.out.println("Ok");
  • if (false) System.out.println("Ok");
  • if (true) System.out.println("Ok");
  • boolean b = false; if (b = true) System.out.println("Ok");

Question 8

Question
Assuming a method contains code which may raise an Exception (but not a Runtime Exception), what is the correct way for a method to indicate that it expects the caller to handle that exception:
Answer
  • throw Exception
  • throws Exception
  • Don't need to specify anything

Question 9

Question
Czy w jednym konstruktorze można wywołać inny konstruktor z tej samej klasy i konstruktor z klasy bazowej jednocześnie?
Answer
  • True
  • False

Question 10

Question
Which variables can an inner class access from the class which encapsulates it?
Answer
  • All static variables
  • All final variables
  • All instance variables
  • Only final instance variables
  • Only final static variables

Question 11

Question
In the following code, which is the earliest statement, where the object originally held in e, may be garbage collected: 1. public class Test { 2. public static void main (String args []) { 3. Employee e = new Employee("Bob", 48); 4. e.calculatePay(); 5. System.out.println(e.printDetails()); 6. e = null; 7. e = new Employee("Denise", 36); 8. e.calculatePay(); 9. System.out.println(e.printDetails()); 10. } 11. }
Answer
  • Line 7
  • Line 8
  • Line 10
  • Line 11
  • Never
  • At the end of function

Question 12

Question
Given the following code what is the effect of a being 5: public class Test { public void add(int a) { loop: for (int i = 1; i < 3; i++){ for (int j = 1; j < 3; j++) { if (a == 5) { break loop; } System.out.println(i * j); } } } }
Answer
  • Generate a runtime error
  • Throw an ArrayIndexOutOfBoundsException
  • Print the values: 1, 2, 2, 4
  • Produces no output

Question 13

Question
What is the result of executing the following fragment of code: boolean flag = false; if (flag = true) { System.out.println("true"); } else { System.out.println("false"); } }
Answer
  • true is printed to standard out
  • false is printed to standard out
  • An exception is raised
  • Nothing happens

Question 14

Question
What will be the output of the program? public class Foo { public static void main(String[] args) { try { return; } finally { System.out.println( "Finally" ); } } }
Answer
  • Finally
  • Compilation fails
  • The code runs with no output.
  • An exception is thrown at runtime.

Question 15

Question
Which of the following are correct. Select the one correct answer.
Answer
  • An import statement, if defined, must always be the first non-comment statement of the file.
  • private members are accessible to all classes in the same package.
  • An abstract class can be declared as final.
  • Local variables cannot be declared as static.

Question 16

Question
Select the one correct answer. Which method defined in Integer class can be used to convert an Integer object to primitive int type.
Answer
  • valueOf
  • intValue
  • getInt
  • getInteger

Question 17

Question
Which code determines the int value data closer to, but not greater than, a double value b?
Answer
  • Int data = (int) Math.floor(b);
  • Int data = (int) Math.abs(b);
  • Int data = (int) Math.ceil(b);
  • Int data = (int) Math.min(b);

Question 18

Question
Which statement is true for the Class java.util.HashSet?
Answer
  • The elements in the collection are unique.
  • The collection is guaranteed to be immutable
  • The elements in the collection are ordered.
  • The elements in the collection are synchronized.

Question 19

Question
What will be the output of the program? public class X { public static void main(String [] args) { try { badMethod(); System.out.print("A"); } catch (Exception ex) { System.out.print("B"); } finally { System.out.print("C"); } System.out.print("D"); } public static void badMethod() { throw new Error(); /* Line 22 */ } }
Answer
  • BC is printed before exiting with an error
  • Compilation fails.
  • ABCD
  • C is printed before exiting with an error message.

Question 20

Question
What is valid returnType for getData? public Class returnData { <returnType> getData(byte a, double z) { return (short)a/z * 10; } }
Answer
  • Short
  • Byte
  • Int
  • Double

Question 21

Question
What is the result? int index = 1; Boolean [] test = new Boolean[3]; Boolean data = test[index];
Answer
  • data has the value of true
  • The code will not compile.
  • data has the value of false
  • data has the value of null

Question 22

Question
What will be the output of the program? class A { final public int GetResult(int a, int b) { return 0; } } class B extends A { public int GetResult(int a, int b) {return 1; } } public class Test { public static void main(String args[]) { B b = new B(); System.out.println("x = " + b.GetResult(0, 1)); } }
Answer
  • x = 0
  • x = 1
  • Compilation fails.
  • An exception is thrown at runtime.

Question 23

Question
class SC2 { public static void main(String [] args) { SC2 s = new SC2(); s.start(); } void start() { int a = 3; int b = 4; System.out.print(" " + 7 + 2 + " "); System.out.print(a + b); System.out.print(" " + a + b + " "); System.out.print(foo() + a + b + " "); System.out.println(a + b + foo()); } String foo() { return "foo"; } }
Answer
  • 9 7 7 foo 7 7foo
  • 72 34 34 foo34 34foo
  • 9 7 7 foo34 34foo
  • 72 7 34 foo34 7foo

Question 24

Question
Float f = new Float("12"); switch (f) { case 12: System.out.println("Twelve"); case 0: System.out.println("Zero"); default: System.out.println("Default"); }
Answer
  • Zero
  • Twelve
  • Default
  • Compilation fails

Question 25

Question
Which statement is true for the class java.util.ArrayList?
Answer
  • The elements in the collection are ordered.
  • The collection is guaranteed to be immutable.
  • The elements in the collection are guaranteed to be unique.
  • The elements in the collection are accessed using a unique key.

Question 26

Question
public class Test { public void foo() { assert false; /* Line 5 */ assert false; /* Line 6 */ } public void bar() { while(true) { assert false; /* Line 12 */ } assert false; /* Line 14 */ } }
Answer
  • Line 5
  • Line 6
  • Line 12
  • Line 14

Question 27

Question
What will be the output of the program? public class Test138 { public static void stringReplace (String text) { text = text.replace ('j' , 'c'); /* Line 5 */ } public static void bufferReplace (StringBuffer text) { text = text.append ("c"); /* Line 9 */ } public static void main (String args[]) { String textString = new String ("java"); StringBuffer textBuffer = new StringBuffer ("java"); /* Line 14 */ stringReplace(textString); bufferReplace(textBuffer); System.out.println (textString + textBuffer); } }
Answer
  • java
  • javac
  • cavajavac
  • javajavac
  • Compile error

Question 28

Question
Which declaration of the main method below would allow a class to be started as a standalone program.
Answer
  • public static int main(char args[])
  • public static void main(String args[])
  • public static void main(String args)
  • public static void main(String... args)

Question 29

Question
Which of these are legal array declarations or definitions?
Answer
  • int[] []x[];
  • int x[5];
  • int *x;
  • None of above

Question 30

Question
Which of the following are keywords in Java.
Answer
  • implement
  • friend
  • NULL
  • synchronized

Question 31

Question
Which of these are legal identifiers.
Answer
  • number_1
  • number_a
  • $1234
  • -volatile

Question 32

Question
The class Hashtable is used to implement which collection interface.
Answer
  • List
  • Set
  • Map
  • SortedSet

Question 33

Question
TreeMap class is used to implement which collection interface. Select the one correct answer.
Answer
  • Set
  • SortedSet
  • Tree
  • SortedMap

Question 34

Question
What gets displayed on the screen when the following program is compiled and run. protected class example { public static void main(String args[]) { String test = "abc"; test = test + test; System.out.println(test); } }
Answer
  • The class does not compile because the top level class cannot be protected.
  • The program prints "abc"
  • The program prints "abcabc"
  • The program does not compile because statement "test = test + test" is illegal.

Question 35

Question
class xyz { static int i; public static void main(String args[]) { while (i < 0) { i--; } System.out.println(i); } }
Answer
  • The program does not compile as i is not initialized.
  • The program prints -1.
  • The program compiles but does not run.
  • The program compiles and runs but does not print anything.
  • The program prints 0.

Question 36

Question
What gets printed on the standard output when the class below is compiled and executed. class A { boolean b = true, f; private void testujemy() { int i = 0; boolean t = true; b = (t || ((i++) == 0)); b = (f || ((i+=2) > 0)); System.out.println(i); } }
Answer
  • 0
  • 1
  • 2
  • 3
  • 4
  • Compilation error
  • Runtime exception.

Question 37

Question
A class can have many methods with the same name as long as the number of parameters or type of parameters is different. This OOP concept is known as
Answer
  • Method Invocating
  • Method Overriding
  • Method Labeling
  • Method Overloading

Question 38

Question
Using up to four characters what is the Java representation of the number 23 in hex?
Answer
  • 0x17
  • 0x18
  • 0x19
  • 0x20

Question 39

Question
What are the two parts of a value of type double?
Answer
  • Length, Denominator
  • Significant Digits, Exponent
  • Mode, Numerator
  • Length, Numerator

Question 40

Question
Using up to four characters, write the Java representation of integer literal 3 in hexadecimal.
Answer
  • 0x03
  • 0x3
  • 0X3
  • 0f3
  • 3

Question 41

Question
What gets printed when the following program is compiled and run. Select the one correct answer. public class test { public static void main(String args[]) { byte x = 3; x = (byte)~x; System.out.println(x); } }
Answer
  • 0
  • 3
  • -4
  • none of these

Question 42

Question
Java endianness is:
Answer
  • Java is big endian
  • Java is little endian

Question 43

Question
What gets displayed on the screen when the following program is compiled and run. Select the one correct answer. public class test { public static void main(String args[]) { int x,y; x = 3 & 5; y = 3 | 5; System.out.println(x + " " + y); } }
Answer
  • 7 1
  • 3 7
  • 1 7
  • 1 3

Question 44

Question
What will be the output of code: switch(3) { case 3: continue; case 4: System.out.println("Case 3 and 4"); break; case 5: System.out.println("Case 5"); }
Answer
  • Case 3 and 4
  • Case 3 and 4 Case 5
  • Runtime exception
  • Compilation error

Question 45

Question
In switch statement the default case must be at the end of switch body.
Answer
  • True
  • False

Question 46

Question
Given two non-negative integers a and b and a String str, what is the number of characters in the expression str.substring(a,b) . Select the one correct answer.
Answer
  • a - b
  • b - a
  • b - a - 1
  • a - b - 1
  • b - a + 1

Question 47

Question
All the wrapper classes (Integer, Boolean, Float, Short, Long, Double and Character) in java are
Answer
  • final
  • private
  • immutable
  • Serializable

Question 48

Question
Consider the following code snippet. What will be assigned to the variable fourthChar, if the code is executed? String str = new String("Java"); char fourthChar = str.charAt(4);
Answer
  • 'a'
  • throws StringIndexOutofBoundsException
  • null characater