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Midterm review. Which of the following correctly initializes array arr to contain four elements each with value 0? I int [] arr = {0, 0, 0, 0}; II int [] arr = new int[4]; III int [] arr = new int[4]; for(int i =0; i < arr.length; i++) arr[i] = 0;.

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slide2

Which of the following correctly initializes array arr to contain four elements each with value 0?

I int [] arr = {0, 0, 0, 0};

II int [] arr = new int[4];

III int [] arr = new int[4];

for(int i =0; i < arr.length; i++) arr[i] = 0;

slide3

Find the index of the first negative integer in arr[0]..arr[N-1], where arr is an array of N integers.

int i = 0;

while ( arr[i] > = 0) { i++; }

location = i ;

The segment will work as intended

  • always
  • never.
  • whenever arr contains at least one negative integer.
  • whenever arr contains at least one nonnegative integer
  • whenever arr contains no negative integers.
slide4

int count = 0;

for (int i =0; i < arr1.length; i++)

if (arr1[i] != 0)

{ arr1[count] = arr1[i];

count ++ ;

}

int[] arr2 = new int[count];

for(int i = 0; i < count ; i++)

arr2[i] = arr1[i];

If array arr1 initially contains the elements 0, 6, 0, 4, 0, 0, 2 in this order, what will arr2 contain after execution of the code segment?

slide5

public static void changeStr(String bStr)

{ bStr="CDE"; }

public static void changeStr(char[] bStr)

{ bStr[0]=\'D\';

bStr[1]=\'E\';

bStr[2]=\'F\'; }

public static void changeStr(char a, char b, char c)

{ a=‘X\';

b=‘Y\';

c=‘Z\'; }

  • P115
slide6

What is wrong with the statement?

int sum = arr[0], i=0;

while ( i < arr.length)

{ i++;

sum =+ arr[i];

}

slide7

for ( int i = 2; i <= k; i++)

if (arr [i] < someValue) System.out.print(“SMALL”);

What is the maximum number of times that SMALL can be printed?

(A)0 (B) 1 (C) k -1 (D) k – 2 (E) k

What is this a worst case?

What is the best case?

slide8

int [] arr = {1, 2, 3, 4};

doSomething(arr);

System.out.print(arr[1] + “ “ );

System.out.print(arr[3]);

public void doSomething(int [] list)

{ int[] b = list;

for (int i = 0; i < b.length; i++)

b[i] = i;

}

slide9

Consider writing a program that produces statistics for long lists of numerical data. Which of the following is the best reason to implement each list with an array of int(or double), rather than an ArrayList of Integer(or Double) object?

  • P245, Q8 and Q9
slide10

List<String> strList = new ArrayList<String>();

String ch = “ “;

Integer intOb = new Integer(5);

Which statement will cause an error?

  • strList.add(ch);
  • strList.add(new String(“handy andy”));
  • strList.add(intOb.toString());
  • strList.add( ch + 8);
  • strList.add(intOb + 8);

What type of data does strList store?

slide11

Which declaration is right? Why?

I List<String> stringList = new ArrayList<String>();

II List<int> intList = new ArrayList<int>();

III ArrayList<Comparable> compList = new ArrayList<Comparable>();

slide12

public class Address

{ private String myName;

private String myStreet;

private String myCity;

private String myZip;

//constructors

//accessors

public String getName(){ /* code 1*/ }

public String getStreet(){ /* code 2*/ }

public String getCity() { /* code 3*/ }

…..

slide13

public class Student

{ private int idNum;

private double gpa;

private Address myAddress;

//constructors ….

//accessors

public Address getAddress()

{ return myAddress; }

public int getIdNum() { return idNum; }

public double getGpa(){ return gpa; }

} P.247-248

slide14

Address[] list = new Address[100];

for (Address a: list)

/* get list of names */

System.out.println(…….

for (Address addr: list)

/* print out a list of address */

slide15

public static boolean match(int [] v, int[] w, int N, int M)

{ int vIndex = 0, wIndex =0;

while (vIndex < N && wIndex < M)

{ if (v[vIndex] == w[wIndex])

return true;

else if (v[vIndex] == w[wIndex] )

vIndex++;

else

wIndex++;

}

return false;

} P252

slide16

public static int mystery(int a, int b)

{ int total =0, count = 1;

while (count <= b)

{ total *= a;

count ++ ;

}

return total;

}

What is the postcondition for method mystery?

slide17

Color(238, 9, 63) would be coded as

  • #EE093F

Which of the following will evaluate to true only if boolean expressions A, B, C are false?

  • !A && !( B && ! C)
  • !A || !B ||!C.
  • !(A || B ||C )
  • !(A && B &&C )
  • !A || !(B ||!C)
slide18

public class Mystery{

public static void strangeMethod(int x, int y)

{ x += y;

y *= x;

System.out.println(x + “ “ + y);

}

public static void main(String [] args)

{ int a = 6, b = 3;

strangeMethod(a, b);

System.out.println(a + “ “ + b)’

} } pass by value? Pass by reference?

slide19

Just before the end of execution, what are the values of x, y and temp?

public class Tester

{ public void someMethod(int a, int b)

{ int temp = a;

a = b;

b = temp; } }

public class TesterMain

{ public static void main(String[] args)

{ int x = 6, y = 8;

Tester tester = new Tester();

tester.someMethod(x, y); }

} scope of a, b, temp, x, y?

slide20

An interface cannot implement any method, wheras an abstract class can => T?

  • A class can implement many interfaces but can have only one superclass => T?
  • An unlimited number of unrelated classes can implement the same interface => T?
  • It is not possible to construct either an abstract class object or an interface object => T?
  • All of the methods in both an abstract class and an interface are public => T?
slide21

Which of the following methods in the Frog class is the best candidate for being a static method. P111

public class Frog

{ private String mySpecies;

private int myAge;

private double myWeight;

private Position myPosition;

private boolean amAlive;

  • swim //frog swims to new position in pond
  • eat //frog eats and gains weight
  • getWeight //returns weight of frog
  • getPondTemperature //return temperature of pond
  • die //frog dies based on frog’s age and pond //temperature
slide22

Which statement is true following execution of the segment?

Temperature t1 = new Temperature(40, “C”);

Temperature t2 = t1;

Temperature t3 = t2.lower(20);

Temperature t4 = t1.toFarenheit()

  • t1, t2, t3 and t4 all have the identical temperature, in degrees Celsius.
  • t1, t2, t3 and t4 all have the identical temperature, in degrees Fahrenheit.
  • t4 represents a Fahrenheit , while t1, t2 and t3 represent all degrees Celsius
  • A NullPointerException was thrown.
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