For example, when your method is added to the class with the main method below, the output should be:

Transcription

1 Sample Problems (from past midterms) 1. Writing Methods, Passing Parameters. Write a method called FindDistance that takes as input four integers, x1, y1, x2, y2, where (x1,y1) and (x2,y2) specify points on a two-dimensional grid. Your method should return as a double the distance between the two points using the formula: 2 + y1 2 x1 x2 y d = ( ) ( ) 2 For example, when your method is added to the class with the main method below, the output should be: class Test // Your method would be inserted here // Sample main method public static void main(string[] args) Test myobj = new Test(); // x1 = 0, y1=0, x2=3, y2=4 System.out.println(myObj.FindDistance(0,0,3,4); // x1 = -2, y1 =0, x2=3, y2=5 System.out.println(myObj.FindDistance(-2,0,3,5);

2 2. Scoping. Given the following program, list all variable names that are directly accessible by name from the places commented as Location. Be sure to include any variables that are members of a class that might be accessible. (Don t worry that the program doesn t actually do anything useful). class C1 public int m_var1; private String m_var2; public void Method1() // Location 1 class C2 private static void Method2(int x1) int b0=0; // Location 2 Method3(x1, b0); private static void Method3(int x2, int x3) int v5; while (x3 < x2) // Location 3 x3++; // Location 4 public static void main(string[] args) int a0; C1 myobj = new C1(); // Location 5 for (int i=0; i<100; i++) int a1; // Location 6 // Location 7 Method2(18);

3 3. Scoping and Parameters. Give the output of the following program when it is compiled and executed. Show your work wherever possible in tracing through the values assigned to all variables for partial credit in the event your final answer is incorrect. class MyNumberClass private int m_num; public MyNumberClass() m_num = 10; public MyNumberClass(int n) m_num = n; public void SetNumber(int n) m_num = n; public int GetNumber() return m_num; class CS201Test public static void main(string[] args) MyNumberClass n1 = new MyNumberClass(); MyNumberClass n2 = new MyNumberClass(5); int n3=0; System.out.println(n1.GetNumber()); System.out.println(n2.GetNumber() + + n3); CS201Test.DoIt(n1, n2, n3); System.out.println( In main: ); System.out.println(n1.GetNumber()); System.out.println(n2.GetNumber() + + n3); public static void DoIt(MyNumberClass x1, MyNumberClass x2, int n3) int temp = x1.getnumber(); n3 = 3; x1.setnumber(x2.getnumber()); x2.setnumber(temp); System.out.println( In DoIt ); System.out.println(x1.GetNumber()); System.out.println(x2.GetNumber() + + n3);

4 4. Implementing the choose function a) The factorial of a nonnegative integer n is written n! and is defined as follows: n! = 1 * 2 * 3 * (n-2) * (n-1) * n and n! = 1 when n = 0 or n = 1 e.g. 1! is equal to 1, 2! is equal to 2, 3! is equal to 6, 4! is equal to 24, etc. Write a static method called factorial that returns the factorial of the number passed in. Use the following class template: class MyMathStuff public static long factorial(long n) // You fill in the code here to make this work properly

5 m b) Written and pronounced m choose n, the choose function is how many n different ways m objects can be chosen from a collection of n objects. For example, for the set of numbers 1,2,3 n=3. If m=2 then we have three ways of choosing two items: 1,2 1,3, 2,3. This function has many applications in statistics and in the analysis of algorithms. m choose n is defined as: m = n n! ( m! )(( n m)! ) Write a static method called choose that returns m choose n. This method should be added to the MyMathStuff class and can invoke the factorial method written in part a. The choose method should input two long values for m and n and return the answer as a long.

6 c) Write a main method that displays the number of the ways we could select items out of a set that varies from 1 to 5 objects. Here is a sample output illustrating the desired behavior: 1 objects can be chosen from 1 objects 1 ways. 1 objects can be chosen from 2 objects 2 ways. 2 objects can be chosen from 2 objects 1 ways. 1 objects can be chosen from 3 objects 3 ways. 2 objects can be chosen from 3 objects 3 ways. 3 objects can be chosen from 3 objects 1 ways. 1 objects can be chosen from 4 objects 4 ways. 2 objects can be chosen from 4 objects 6 ways. 3 objects can be chosen from 4 objects 4 ways. 4 objects can be chosen from 4 objects 1 ways. 1 objects can be chosen from 5 objects 5 ways. 2 objects can be chosen from 5 objects 10 ways. 3 objects can be chosen from 5 objects 10 ways. 4 objects can be chosen from 5 objects 5 ways. 5 objects can be chosen from 5 objects 1 ways.

7 5. Arrays. Use the following method heading for FindMin. This method is passed a 2D array of integers and returns an object of type Coord: public static Coord FindMin(int[][] arr) Here is the Coord class: public class Coord public int row, column; public Coord(int r, int c) row = r; column = c; Write the method FindMin so that it returns the coordinate of the smallest value in the 2D array. For example: public static void main(string[] args) int[][] arr = new int[10][10]; Coord c = null; // Initialize array to zero for (int i=0; i<10; i++) for (int j=0; j<10; j++) arr[i][j]=0; arr[5][3] = -4; // Set one value to -4 c = FindMin(arr); System.out.println( Min at + c.row + + c.column + Val = + arr[c.row][c.column]); This program should output: Min at 5 3 Val = -4