1. Java Professionals
Community BY
Celebrating anniversary!

2. Призы от партнеров:

3. 1a. Reflection

4. import java.lang.reflect.Field;
import java.lang.reflect.Modifier;
public class C_Reflection {
public static final String s = "one";
public static void main(String[] args) throws NoSuchFieldException, IllegalAccessException
{
Field field = C_Reflection.class.getField("s");
int modifiers = field.getModifiers();
Field modifierField = field.getClass().getDeclaredField("modifiers");
modifiers = modifiers & ~Modifier.FINAL;
modifierField.setAccessible(true);
modifierField.setInt(field, modifiers);
field.set(null, "two");
System.out.println(s);
}
}

5. import java.lang.reflect.Field;
import java.lang.reflect.Modifier;
public class C_Reflection {
public static final String s = "one";
public static void main(String[] args) throws NoSuchFieldException, IllegalAccessException
{
Field field = C_Reflection.class.getField("s");
int modifiers = field.getModifiers();
Field modifierField = field.getClass().getDeclaredField("modifiers");
modifiers = modifiers & ~Modifier.FINAL;
modifierField.setAccessible(true);
modifierField.setInt(field, modifiers);
field.set(null, "two");
System.out.println(s);
}
}
A. one
B. two
C. NoSuchFieldException
D. IllegalAccessException

6. 1b. Classloading

7. class Parent {
public static final String value = "Parent value";
static {
System.out.println("Parent static");
}
}
class Child extends Parent {
static {
System.out.println("Child static");
}
{
System.out.println("Child initializer");
}
}
public class A_Classload {
public static void main(String[] args) {
System.out.println(Child.value);
}
}

8. class Parent {
public static final String value = "Parent value";
static {
System.out.println("Parent static");
}
}
class Child extends Parent {
static {
System.out.println("Child static");
}
{
System.out.println("Child initializer");
}
}
public class A_Classload {
public static void main(String[] args) {
System.out.println(Child.value);
}
}
A. Parent value
B. Parent static Parent value
C. Parent static Child static Parent value
D. Parent static Child static Child initializer Parent value

9. 1c. Lists

10. import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;
public class D_Lists {
public static final int MAX_VAL = 10000;
public static void main(String[] args) {
List<Integer> linkedList = new LinkedList<>();
List<Integer> arrayList = new ArrayList<>();
for(int i = 0; i < MAX_VAL; i++) {
linkedList.add(i);
arrayList.add(i);
}
long linkedListTime = System.nanoTime();
for(int i = 0; i < MAX_VAL; i++) {
linkedList.add(MAX_VAL/2, i);
}
linkedListTime = System.nanoTime() - linkedListTime;
long arrayListTime = System.nanoTime();
for(int i = 0; i < MAX_VAL; i++) {
arrayList.add(MAX_VAL/2, i);
}
arrayListTime = System.nanoTime() - arrayListTime;
if (arrayListTime < linkedListTime) {
System.out.println("ARRAY LIST WINS!");
} else {
System.out.println("LINKED LIST WINS!");
}
}
}

11. import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;
public class D_Lists {
public static final int MAX_VAL = 10000;
public static void main(String[] args) {
List<Integer> linkedList = new LinkedList<>();
List<Integer> arrayList = new ArrayList<>();
for(int i = 0; i < MAX_VAL; i++) {
linkedList.add(i);
arrayList.add(i);
}
long linkedListTime = System.nanoTime();
for(int i = 0; i < MAX_VAL; i++) {
linkedList.add(MAX_VAL/2, i);
}
linkedListTime = System.nanoTime() - linkedListTime;
long arrayListTime = System.nanoTime();
for(int i = 0; i < MAX_VAL; i++) {
arrayList.add(MAX_VAL/2, i);
}
arrayListTime = System.nanoTime() - arrayListTime;
if (arrayListTime < linkedListTime) {
System.out.println("ARRAY LIST WINS!");
} else {
System.out.println("LINKED LIST WINS!");
}
}
}
A. ARRAY LIST WINS!
B. LINKED LIST WINS!
C. StackOverflowException
D. Не скомпилируется

12. 1. Final

13. import java.util.Random;
public class P_Even {
public static void main(String[] args) {
Random random = new Random();
for (int i = 0; i < 100; i++) {
int x = Math.abs(random.nextInt());
if (isEvenBase(x) != isEvenTest(x)) {
throw new RuntimeException("Fail! " + x);
}
}
}
// do not ban: 'x', '(', ')', '=', '0', '1', '2'
// ban:
static boolean isEvenBase(int x) {
return x % 2 == 0;
}
static boolean isEvenTest(int x) {
return true;
}
}

14. 2. Complexity

15. import java.math.BigInteger;
import java.security.SecureRandom;
public class R_Complexity {
public static final String NEARLY_INDEFINITE = "...";
public static void main(String[] args) {
System.out.println(foo(1));
}
public static String foo(int n) {
String temp = "";
for (int i = 0; i < n; i++) {
for (int j = i; j < n; j++) {
temp += NEARLY_INDEFINITE.charAt(j);
}
}
return temp;
}
}

16. import java.math.BigInteger;
import java.security.SecureRandom;
public class R_Complexity {
public static final String NEARLY_INDEFINITE = "...";
public static void main(String[] args) {
System.out.println(foo(1));
}
public static String foo(int n) {
String temp = "";
for (int i = 0; i < n; i++) {
for (int j = i; j < n; j++) {
temp += NEARLY_INDEFINITE.charAt(j);
}
}
return temp;
}
}
A. O(n)
B. O(n^2)
C. O(n^4)
D. O(n!)

17. 3. Exception

18. import java.util.Arrays;
import java.util.ConcurrentModificationException;
import java.util.List;
public class B_Exception {
public static void main(String[] args) {
List<String> list = Arrays.asList("one", "two");
try {
for (String s : list) {
list.remove(s);
}
} catch (ConcurrentModificationException ex) {
System.out.println("1");
} catch (RuntimeException ex) {
System.out.println("2");
} catch (Exception ex) {
System.out.println("3");
} catch (Throwable ex) {
System.out.println("4");
}
}
}

19. import java.util.Arrays;
import java.util.ConcurrentModificationException;
import java.util.List;
public class B_Exception {
public static void main(String[] args) {
List<String> list = Arrays.asList("one", "two");
try {
for (String s : list) {
list.remove(s);
}
} catch (ConcurrentModificationException ex) {
System.out.println("1");
} catch (RuntimeException ex) {
System.out.println("2");
} catch (Exception ex) {
System.out.println("3");
} catch (Throwable ex) {
System.out.println("4");
}
}
}
A. 1
B. 2
C. 3
D. 4

20. Generics

21. import java.util.ArrayList;
import java.util.Collection;
import java.util.List;
public class E_Generics {
public static void main(String[] args) {
List<Integer> list = new ArrayList<>();
insert(list, "123");
System.out.println(list);
}
public static void insert(List l, Object o) {
l.add(o);
}
}

22. import java.util.ArrayList;
import java.util.Collection;
import java.util.List;
public class E_Generics {
public static void main(String[] args) {
List<Integer> list = new ArrayList<>();
insert(list, "123");
System.out.println(list);
}
public static void insert(List l, Object o) {
l.add(o);
}
}
A. []
B. [123]
C. ClassCastException
D. Не скомпилируется

23. Спасибо!
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