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

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OCAJP7

Question 1 of 48

1

Which of the following is illegal:

Select one of the following:

  • int i = 32;

  • float f = 45.0;

  • double d = 45.0;

Explanation

Question 2 of 48

1

public class Test {
static int age;
public static void main (String args []) {
age = age + 1;
System.out.println("The age is " + age);
}
}

Select one of the following:

  • 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

Explanation

Question 3 of 48

1

public static void main(String[] args) {
int age;
System.out.println(age+1);
}

Select one of the following:

  • 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

Explanation

Question 4 of 48

1

Which of the following return true?

Select one or more of the following:

  • "john" == "john"

  • "john".equals("john")

  • "john" = "john"

  • "john".equals(new Button("john"))

Explanation

Question 5 of 48

1

Which of the following is correct:

Select one or more of the following:

  • 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"};

Explanation

Question 6 of 48

1

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

Select one of the following:

  • True
  • False

Explanation

Question 7 of 48

1

Which of the following are acceptable to the Java 7 compiler?

Select one or more of the following:

  • 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");

Explanation

Question 8 of 48

1

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:

Select one of the following:

  • throw Exception

  • throws Exception

  • Don't need to specify anything

Explanation

Question 9 of 48

1

Czy w jednym konstruktorze można wywołać inny konstruktor z tej samej klasy i konstruktor z klasy bazowej jednocześnie?

Select one of the following:

  • True
  • False

Explanation

Question 10 of 48

1

Which variables can an inner class access from the class which encapsulates it?

Select one or more of the following:

  • All static variables

  • All final variables

  • All instance variables

  • Only final instance variables

  • Only final static variables

Explanation

Question 11 of 48

1

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. }

Select one of the following:

  • Line 7

  • Line 8

  • Line 10

  • Line 11

  • Never

  • At the end of function

Explanation

Question 12 of 48

1

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);
}
}
}
}

Select one of the following:

  • Generate a runtime error

  • Throw an ArrayIndexOutOfBoundsException

  • Print the values: 1, 2, 2, 4

  • Produces no output

Explanation

Question 13 of 48

1

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");
}
}

Select one of the following:

  • true is printed to standard out

  • false is printed to standard out

  • An exception is raised

  • Nothing happens

Explanation

Question 14 of 48

1

What will be the output of the program?

public class Foo
{
public static void main(String[] args)
{
try
{
return;
}
finally
{
System.out.println( "Finally" );
}
}
}

Select one of the following:

  • Finally

  • Compilation fails

  • The code runs with no output.

  • An exception is thrown at runtime.

Explanation

Question 15 of 48

1

Which of the following are correct. Select the one correct answer.

Select one of the following:

  • 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.

Explanation

Question 16 of 48

1

Select the one correct answer. Which method defined in Integer class can be used to convert an Integer object to primitive int type.

Select one of the following:

  • valueOf

  • intValue

  • getInt

  • getInteger

Explanation

Question 17 of 48

1

Which code determines the int value data closer to, but not greater than, a double value b?

Select one of the following:

  • Int data = (int) Math.floor(b);

  • Int data = (int) Math.abs(b);

  • Int data = (int) Math.ceil(b);

  • Int data = (int) Math.min(b);

Explanation

Question 18 of 48

1

Which statement is true for the Class java.util.HashSet?

Select one of the following:

  • 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.

Explanation

Question 19 of 48

1

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 */
}
}

Select one of the following:

  • BC is printed before exiting with an error

  • Compilation fails.

  • ABCD

  • C is printed before exiting with an error message.

Explanation

Question 20 of 48

1

What is valid returnType for getData?
public Class returnData
{
<returnType> getData(byte a, double z)
{
return (short)a/z * 10;
}
}

Select one of the following:

  • Short

  • Byte

  • Int

  • Double

Explanation

Question 21 of 48

1

What is the result?
int index = 1;
Boolean [] test = new Boolean[3];
Boolean data = test[index];

Select one of the following:

  • data has the value of true

  • The code will not compile.

  • data has the value of false

  • data has the value of null

Explanation

Question 22 of 48

1

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));
}
}

Select one of the following:

  • x = 0

  • x = 1

  • Compilation fails.

  • An exception is thrown at runtime.

Explanation

Question 23 of 48

1

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";
}
}

Select one of the following:

  • 9 7 7 foo 7 7foo

  • 72 34 34 foo34 34foo

  • 9 7 7 foo34 34foo

  • 72 7 34 foo34 7foo

Explanation

Question 24 of 48

1

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

Select one of the following:

  • Zero

  • Twelve

  • Default

  • Compilation fails

Explanation

Question 25 of 48

1

Which statement is true for the class java.util.ArrayList?

Select one of the following:

  • 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.

Explanation

Question 26 of 48

1

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 */
}
}

Select one of the following:

  • Line 5

  • Line 6

  • Line 12

  • Line 14

Explanation

Question 27 of 48

1

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);
}
}

Select one of the following:

  • java

  • javac

  • cavajavac

  • javajavac

  • Compile error

Explanation

Question 28 of 48

1

Which declaration of the main method below would allow a class to be started as a standalone program.

Select one or more of the following:

  • public static int main(char args[])

  • public static void main(String args[])

  • public static void main(String args)

  • public static void main(String... args)

Explanation

Question 29 of 48

1

Which of these are legal array declarations or definitions?

Select one of the following:

  • int[] []x[];

  • int x[5];

  • int *x;

  • None of above

Explanation

Question 30 of 48

1

Which of the following are keywords in Java.

Select one of the following:

  • implement

  • friend

  • NULL

  • synchronized

Explanation

Question 31 of 48

1

Which of these are legal identifiers.

Select one or more of the following:

  • number_1

  • number_a

  • $1234

  • -volatile

Explanation

Question 32 of 48

1

The class Hashtable is used to implement which collection interface.

Select one of the following:

  • List

  • Set

  • Map

  • SortedSet

Explanation

Question 33 of 48

1

TreeMap class is used to implement which collection interface. Select the one correct answer.

Select one of the following:

  • Set

  • SortedSet

  • Tree

  • SortedMap

Explanation

Question 34 of 48

1

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);
}
}

Select one of the following:

  • 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.

Explanation

Question 35 of 48

1

class xyz {
static int i;
public static void main(String args[]) {
while (i < 0) {
i--;
}
System.out.println(i);
}
}

Select one of the following:

  • 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.

Explanation

Question 36 of 48

1

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);
}
}

Select one of the following:

  • 0

  • 1

  • 2

  • 3

  • 4

  • Compilation error

  • Runtime exception.

Explanation

Question 37 of 48

1

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

Select one of the following:

  • Method Invocating

  • Method Overriding

  • Method Labeling

  • Method Overloading

Explanation

Question 38 of 48

1

Using up to four characters what is the Java representation of the number 23 in hex?

Select one of the following:

  • 0x17

  • 0x18

  • 0x19

  • 0x20

Explanation

Question 39 of 48

1

What are the two parts of a value of type double?

Select one of the following:

  • Length, Denominator

  • Significant Digits, Exponent

  • Mode, Numerator

  • Length, Numerator

Explanation

Question 40 of 48

1

Using up to four characters, write the Java representation of integer literal 3 in hexadecimal.

Select one or more of the following:

  • 0x03

  • 0x3

  • 0X3

  • 0f3

  • 3

Explanation

Question 41 of 48

1

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);
}
}

Select one of the following:

  • 0

  • 3

  • -4

  • none of these

Explanation

Question 42 of 48

1

Java endianness is:

Select one of the following:

  • Java is big endian

  • Java is little endian

Explanation

Question 43 of 48

1

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);
}
}

Select one of the following:

  • 7 1

  • 3 7

  • 1 7

  • 1 3

Explanation

Question 44 of 48

1

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");
}

Select one of the following:

  • Case 3 and 4

  • Case 3 and 4
    Case 5

  • Runtime exception

  • Compilation error

Explanation

Question 45 of 48

1

In switch statement the default case must be at the end of switch body.

Select one of the following:

  • True
  • False

Explanation

Question 46 of 48

1

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.

Select one of the following:

  • a - b

  • b - a

  • b - a - 1

  • a - b - 1

  • b - a + 1

Explanation

Question 47 of 48

1

All the wrapper classes (Integer, Boolean, Float, Short, Long, Double and Character) in java are

Select one or more of the following:

  • final

  • private

  • immutable

  • Serializable

Explanation

Question 48 of 48

1

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);

Select one of the following:

  • 'a'

  • throws StringIndexOutofBoundsException

  • null characater

Explanation