Practice Operators and Assignments –
What will be the output of the program?
import java.util.*;
class H {
public static void main (String[] args) {
Object x = new Vector().elements();
System.out.print((x instanceof Enumeration)+",");
System.out.print((x instanceof Iterator)+",");
System.out.print(x instanceof ListIterator);
}
}
Which two statements are true about wrapper or&n
Practice Java.lang Class –
Which two statements are true about wrapper or String classes?
What will be the output of the program (in jdk1.6 or above)?
Practice Java.lang Class –
What will be the output of the program (in jdk1.6 or above)?
public class BoolTest {
public static void main(String [] args) {
Boolean b1 = new Boolean("false");
boolean b2;
b2 = b1.booleanValue();
if (!b2) {
b2 = true;
System.out.print("x");
}
if (b1 & b2) /* Line 13 */ {
System.out.print("y ");
}
System.out.println("z");
}
}
Practice Java.lang Class –
What will be the output of the program?
try {
Float f1 = new Float("3.0");
int x = f1.intValue();
byte b = f1.byteValue();
double d = f1.doubleValue();
System.out.println(x + b + d);
}
catch (NumberFormatException e) /* Line 9 */ {
System.out.println("bad number"); /* Line 11 */
}
Practice Java.lang Class –
What will be the output of the program?
public class BoolTest {
public static void main(String [] args) {
int result = 0;
Boolean b1 = new Boolean("TRUE");
Boolean b2 = new Boolean("true");
Boolean b3 = new Boolean("tRuE");
Boolean b4 = new Boolean("false");
if (b1 == b2) /* Line 10 */
result = 1;
if (b1.equals(b2) ) /* Line 12 */
result = result + 10;
if (b2 == b4) /* Line 14 */
result = result + 100;
if (b2.equals(b4) ) /* Line 16 */
result = result + 1000;
if (b2.equals(b3) ) /* Line 18 */
result = result + 10000;
System.out.println("result = " + result);
}
}
Practice Java.lang Class –
What will be the output of the program?
public class WrapTest {
public static void main(String [] args) {
int result = 0;
short s = 42;
Long x = new Long("42");
Long y = new Long(42);
Short z = new Short("42");
Short x2 = new Short(s);
Integer y2 = new Integer("42");
Integer z2 = new Integer(42);
if (x == y) /* Line 13 */
result = 1;
if (x.equals(y) ) /* Line 15 */
result = result + 10;
if (x.equals(z) ) /* Line 17 */
result = result + 100;
if (x.equals(x2) ) /* Line 19 */
result = result + 1000;
if (x.equals(z2) ) /* Line 21 */
result = result + 10000;
System.out.println("result = " + result);
}
}
Practice Exceptions –
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() {
}
}
Practice Exceptions –
What will be the output of the program?
public class X {
public static void main(String [] args) {
try {
badMethod();
System.out.print("A");
}
catch (RuntimeException ex) /* Line 10 */ {
System.out.print("B");
}
catch (Exception ex1) {
System.out.print("C");
}
finally {
System.out.print("D");
}
System.out.print("E");
}
public static void badMethod() {
throw new RuntimeException();
}
}
Practice Exceptions –
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 */
}
}
Practice Exceptions –
What will be the output of the program?
try {
int x = 0;
int y = 5 / x;
}
catch (Exception e) {
System.out.println("Exception");
}
catch (ArithmeticException ae) {
System.out.println(" Arithmetic Exception");
}
System.out.println("finished");
Practice Exceptions –
What will be the output of the program?
public class Foo {
public static void main(String[] args) {
try {
return;
}
finally {
System.out.println( "Finally" );
}
}
}
public Object m()
{
Practice Garbage Collections –
public Object m()
{
Object o = new Float(3.14F);
Object [] oa = new Object[l];
oa[0] = o; /* Line 5 */
o = null; /* Line 6 */
oa[0] = null; /* Line 7 */
return o; /* Line 8 */
} When is the Float object, created in line 3, eligible for garbage collection?
public class X {
public
Practice Garbage Collections –
public class X {
public static void main(String [] args) {
X x = new X();
X x2 = m1(x); /* Line 6 */
X x4 = new X();
x2 = x4; /* Line 8 */
doComplexStuff();
}
static X m1(X mx) {
mx = new X();
return mx;
}
} After line 8 runs. how many objects are eligible for garbage collection?
class Test {
private
Practice Garbage Collections –
class Test {
private Demo d;
void start() {
d = new Demo();
this.takeDemo(d); /* Line 7 */
} /* Line 8 */
void takeDemo(Demo demo) {
demo = null;
demo = new Demo();
}
} When is the Demo object eligible for garbage collection?
class Bar { }
class Test {
Practice Garbage Collections –
class Bar { }
class Test {
Bar doBar() {
Bar b = new Bar(); /* Line 6 */
return b; /* Line 7 */
}
public static void main (String args[]) {
Test t = new Test(); /* Line 11 */
Bar newBar = t.doBar(); /* Line 12 */
System.out.println("newBar");
newBar = new Bar(); /* Line 14 */
System.out.println("finishing"); /* Line 15 */
}
} At what point is the Bar object, created on line 6, eligible for garbage collection?