Explore topic-wise MCQs in Engineering.

Which of the following statements about the hashcode() method are incorrect?

1. The value returned by hashcode() is used in some collection classes to help locate objects.
2. The hashcode() method is required to return a positive int value.
3. The hashcode() method in the String class is the one inherited from Object.
4. Two new empty String objects will produce identical hashcodes.

What will be the output of the program?

public class NFE { public static void main(String [] args) { String s = "42"; try { s = s.concat(".5"); /* Line 8 */ double d = Double.parseDouble(s); s = Double.toString(d); int x = (int) Math.ceil(Double.valueOf(s).doubleValue()); System.out.println(x); } catch (NumberFormatException e) { System.out.println("bad number"); } }
}

What will be the output of the program?

interface Count { short counter = 0; void countUp();
}
public class TestCount implements Count { public static void main(String [] args) { TestCount t = new TestCount(); t.countUp(); } public void countUp() { for (int x = 6; x>counter; x--, ++counter) /* Line 14 */ { System.out.print(" " + counter); } }
}

What will be the output of the program?

class Base
{ Base() { System.out.print("Base"); }
} public class Alpha extends Base
{ public static void main(String[] args) { new Alpha(); /* Line 12 */ new Base(); /* Line 13 */ } }

What will be the output of the program?

import java.util.*;
public class NewTreeSet2 extends NewTreeSet { public static void main(String [] args) { NewTreeSet2 t = new NewTreeSet2(); t.count(); }
}
protected class NewTreeSet
{ void count() { for (int x = 0; x < 7; x++,x++ ) { System.out.print(" " + x); } }
}

What will be the output of the program?

class Super { public Integer getLength() { return new Integer(4); } } public class Sub extends Super { public Long getLength() { return new Long(5); } public static void main(String[] args) { Super sooper = new Super(); Sub sub = new Sub(); System.out.println( sooper.getLength().toString() + "," + sub.getLength().toString() ); } }

x = 0;
if (x1.hashCode() != x2.hashCode() ) x = x + 1;
if (x3.equals(x4) ) x = x + 10;
if (!x5.equals(x6) ) x = x + 100;
if (x7.hashCode() == x8.hashCode() ) x = x + 1000;
System.out.println("x = " + x);

Which of the following are true statements?

1. The Iterator interface declares only three methods: hasNext, next and remove.
2. The ListIterator interface extends both the List and Iterator interfaces.
3. The ListIterator interface provides forward and backward iteration capabilities.
4. The ListIterator interface provides the ability to modify the List during iteration.
5. The ListIterator interface provides the ability to determine its position in the List.

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

What will be the output of the program?

System.out.println(Math.sqrt(-4D));

What will be the output of the program?

String a = "newspaper";
a = a.substring(5,7);
char b = a.charAt(1);
a = a + b;
System.out.println(a);

What will be the output of the program?

public class StringRef { public static void main(String [] args) { String s1 = "abc"; String s2 = "def"; String s3 = s2; /* Line 7 */ s2 = "ghi"; System.out.println(s1 + s2 + s3); }
}

What will be the output of the program?

public class ExamQuestion7 { static int j; static void methodA(int i) { boolean b; do { b = i<10 | methodB(4); /* Line 9 */ b = i<10 || methodB(8); /* Line 10 */ }while (!b); } static boolean methodB(int i) { j += i; return true; } public static void main(String[] args) { methodA(0); System.out.println( "j = " + j ); } }

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 */
}

What will be the output of the program?

class Q207 { public static void main(String[] args) { int i1 = 5; int i2 = 6; String s1 = "7"; System.out.println(i1 + i2 + s1); /* Line 8 */ } }

What will be the output of the program?

public class SqrtExample { public static void main(String [] args) { double value = -9.0; System.out.println( Math.sqrt(value)); }
}

What will be the output of the program?

String s = "ABC"; s.toLowerCase(); s += "def"; System.out.println(s);

What will be the output of the program?

public class Test { public static void main(String[] args) { final StringBuffer a = new StringBuffer(); final StringBuffer b = new StringBuffer(); new Thread() { public void run() { System.out.print(a.append("A")); synchronized(b) { System.out.print(b.append("B")); } } }.start(); new Thread() { public void run() { System.out.print(b.append("C")); synchronized(a) { System.out.print(a.append("D")); } } }.start(); } }

What will be the output of the program?

String s = "hello"; Object o = s; if( o.equals(s) )
{ System.out.println("A"); } else
{ System.out.println("B"); } if( s.equals(o) )
{ System.out.println("C"); } else
{ System.out.println("D"); }

1. A
2. B
3. C
4. D

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"); }
}

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); } }

What will be the output of the program?

class Tree { } class Pine extends Tree { } class Oak extends Tree { } public class Forest1 { public static void main (String [] args) { Tree tree = new Pine(); if( tree instanceof Pine ) System.out.println ("Pine"); else if( tree instanceof Tree ) System.out.println ("Tree"); else if( tree instanceof Oak ) System.out.println ( "Oak" ); else System.out.println ("Oops "); } }

What will be the output of the program?

String d = "bookkeeper";
d.substring(1,7);
d = "w" + d;
d.append("woo"); /* Line 4 */
System.out.println(d);

What will be the output of the program?

String a = "ABCD"; String b = a.toLowerCase(); b.replace('a','d'); b.replace('b','c'); System.out.println(b);

What will be the output of the program?

public class ExamQuestion6 { static int x; boolean catch() { x++; return true; } public static void main(String[] args) { x=0; if ((catch() | catch()) || catch()) x++; System.out.println(x); } }

What will be the output of the program?

public class Test178 { public static void main(String[] args) { String s = "foo"; Object o = (Object)s; if (s.equals(o)) { System.out.print("AAA"); } else { System.out.print("BBB"); } if (o.equals(s)) { System.out.print("CCC"); } else { System.out.print("DDD"); } } }

What will be the output of the program?

String x = "xyz";
x.toUpperCase(); /* Line 2 */
String y = x.replace('Y', 'y');
y = y + "abc";
System.out.println(y);

What will be the output of the program?

int i = (int) Math.random();

What will be the output of the program?

class A { public A(int x){} } class B extends A { } public class test { public static void main (String args []) { A a = new B(); System.out.println("complete"); } }

What will be the output of the program?

int i = 1, j = 10; do { if(i++ > --j) /* Line 4 */ { continue; } } while (i < 5); System.out.println("i = " + i + "and j = " + j); /* Line 9 */

What two statements are true about properly overridden hashCode() and equals() methods?

1. hashCode() doesn't have to be overridden if equals() is.
2. equals() doesn't have to be overridden if hashCode() is.
3. hashCode() can always return the same value, regardless of the object that invoked it.
4. equals() can be true even if it's comparing different objects.

Which two statements are true about comparing two instances of the same class, given that the equals() and hashCode() methods have been properly overridden?

1. If the equals() method returns true, the hashCode() comparison == must return true.
2. If the equals() method returns false, the hashCode() comparison != must return true.
3. If the hashCode() comparison == returns true, the equals() method must return true.
4. If the hashCode() comparison == returns true, the equals() method might return true.

Which collection class allows you to associate its elements with key values, and allows you to retrieve objects in FIFO (first-in, first-out) sequence?

Which interface provides the capability to store objects using a key-value pair?

Which collection class allows you to access its elements by associating a key with an element's value, and provides synchronization?

Which is valid declaration of a float?

/* Missing Statement ? */
public class foo { public static void main(String[]args)throws Exception { java.io.PrintWriter out = new java.io.PrintWriter(); new java.io.OutputStreamWriter(System.out,true); out.println("Hello"); } }

What is the numerical range of char?

Which of the following are Java reserved words?

1. run
2. import
3. default
4. implement

interface DoMath { double getArea(int rad); }
interface MathPlus { double getVol(int b, int h); }
/* Missing Statements ? */

1. class AllMath extends DoMath { double getArea(int r); }
2. interface AllMath implements MathPlus { double getVol(int x, int y); }
3. interface AllMath extends DoMath { float getAvg(int h, int l); }
4. class AllMath implements MathPlus { double getArea(int rad); }
5. abstract class AllMath implements DoMath, MathPlus { public double getArea(int rad) { return rad * rad * 3.14; } }

Which two statements are true for any concrete class implementing the java.lang.Runnable interface?

1. You can extend the Runnable interface as long as you override the public run() method.
2. The class must contain a method called run() from which all code for that thread will be initiated.
3. The class must contain an empty public void method named run().
4. The class must contain a public void method named runnable().
5. The class definition must include the words implements Threads and contain a method called run().
6. The mandatory method must be public, with a return type of void, must be called run(), and cannot take any arguments.

/* Missing statements ? */
public class NewTreeSet extends java.util.TreeSet
{ public static void main(String [] args) { java.util.TreeSet t = new java.util.TreeSet(); t.clear(); } public void clear() { TreeMap m = new TreeMap(); m.clear(); }
}

1. No statement is required
2. import java.util.*;
3. import.java.util.Tree*;
4. import java.util.TreeSet;
5. import java.util.TreeMap;

Which three statements are true?

1. The default constructor initialises method variables.
2. The default constructor has the same access as its class.
3. The default constructor invokes the no-arg constructor of the superclass.
4. If a class lacks a no-arg constructor, the compiler always creates a default constructor.
5. The compiler creates a default constructor only when there are no other constructors for the class.

package testpkg.p1;
public class ParentUtil { public int x = 420; protected int doStuff() { return x; }
} package testpkg.p2;
import testpkg.p1.ParentUtil;
public class ChildUtil extends ParentUtil { public static void main(String [] args) { new ChildUtil().callStuff(); } void callStuff() { System.out.print("this " + this.doStuff() ); /* Line 18 */ ParentUtil p = new ParentUtil(); System.out.print(" parent " + p.doStuff() ); /* Line 20 */ }
}

Which three are valid method signatures in an interface?

1. private int getArea();
2. public float getVol(float x);
3. public void main(String [] args);
4. public static void main(String [] args);
5. boolean setFlag(Boolean [] test);

What will be the output of the program?

String x = new String("xyz");
String y = "abc";
x = x + y;

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); }
}

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); }
}

What will be the output of the program?

public class ObjComp { public static void main(String [] args ) { int result = 0; ObjComp oc = new ObjComp(); Object o = oc; if (o == oc) result = 1; if (o != oc) result = result + 10; if (o.equals(oc) ) result = result + 100; if (oc.equals(o) ) result = result + 1000; System.out.println("result = " + result); }
}

What will be the output of the program?

public class Example { public static void main(String [] args) { double values[] = {-2.3, -1.0, 0.25, 4}; int cnt = 0; for (int x=0; x < values.length; x++) { if (Math.round(values[x] + .5) == Math.ceil(values[x])) { ++cnt; } } System.out.println("same results " + cnt + " time(s)"); }
}