Introduction to Java Unit 6. Exercises: Arrays

Transcription

1 Introduction to Java Unit 6. Exercises: Arrays 1. What is displayed? int [] cosmic = { 3, 6, 5, 8 ; System.out.println( cosmic[ 2 ] ); 2. What is displayed? String [] gamma = { "do", "re", "mi" ; System.out.println( gamma.length ); 3. What is displayed? String [] arr = { "one", "five", "eight" ; System.out.println( arr[ 1 ] ); 4. What is displayed? int [] arr = { 5, 88, 1 ; for ( int n = 0; n <= 2; n++) System.out.print( arr[n] + " " ); 5. What is displayed? int [] arr = { 70, 6, 2 ; for ( int n = 2; n >= 0; n--) System.out.print( arr[n] + " " ); 6. What is displayed? double [] ray = new double[ 4 ]; ray[2] = 5.2; ray[0] = -9; ray[3] = 14.5; ray[1] = 0.0; for ( int n = 0; n < ray.length; n++ ) System.out.println( ray[ n ] ); 7. What is displayed? int [] arr = new int[4]; arr[ k ] = 3*k; System.out.println( arr[ k ] ); 8. What is displayed? int [] arr = new int[5]; for (int k = arr.length - 1; k >= 0; k-- ) arr[ k ] = 10 - k; System.out.println( arr[ k ] ); 9. What is displayed? int x = 0; int [] arr = { 5, -5, 7, 1 ; for ( int n = 0; n < arr.length; n++) x = x + arr[ n ]; System.out.println( x ); Page 1

2 10. If a is { 5, 8, 6, 7, what does this method return? 11. If a is { 13, does this method crash? If yes, why? If no, what does the 12. If a is { 188.7, 54.8, 77.2, what does this 13. If a is { -6.3, -32.1, -4, -6.2, what does this 14. If a is { 8, 12, 14, 9, what does this 15. Give an example of an array that will cause this method to return a C. 16. If a is { 1, 2, 3, 4, what are the contents of the array that is returned? 17. If a is { 5, 6, 6, 5, 7, what does this 18. If a is { 40, 30, 29, 12, what does this 19. If a is { 8, what does this method return? 20. Give an example of an array that causes this method to return true. The array must have a length of 4. public int m33( int [] a ) { int m = a[0]; for ( int n = 1; n < a.length; n++ ){ if ( a[n] > m ) m = a[n]; return m; public double m99( double [] a ){ double mm = 0; for ( int i = 0; i < a.length; i++ ){ if ( a[i] > mm ) mm = a[i]; return mm; public String met6( int [] a ){ for ( int k = 0; k < a.length; k++ ){ if ( a[k] > 10 ) return "A"; else return "B"; return "C"; public int [] met6( int [] a ){ int [] b = new int[ a.length ]; int n = a.length-1; for ( int k = 0; k < a.length; k++ ){ b[n] = a[k]; n--; return b; public boolean m77( int [] a ){ for ( int i = 0; i < a.length-1; i++ ){ if ( a[i] >= a[i+1] ) return false; return true; public boolean m66( int [] a ){ for ( int i = 0; i < a.length-1; i++ ){ if ( a[i]+ 1!= a[i+1] ) return false; return true; Page 2

3 21. If a is { 9, 5, 4, 6, 5, 7, what does this public int m55( int [] a ) { int k = 0; for ( int n = 1; n < a.length; n++ ){ if ( a[n] < a[k] ) k = n; return k; The following questions deal with arrays of Strings and other objects. 22. This method compiles. If the array is { "Look!", "four", "barges" what does the public String met( String [] a ){ String s = a[2].substring( 0, 2 ); return s; 23. What two conditions must be true for this method to run without crashing? 24. How many Dog objects does line 1 create? a) 5 Dog objects b) 6 Dog objects c) 7 Dog objects d) 0 Dog objects 25. These two lines do compile but crash when you try to run it. What s the problem? 1 2 In a main method Dog [] d = new Dog[6]; int num = d[2].get(); public class Dog{ private int age; public Dog( int a){ age = a; public int get(){ return age; 26. This method does not compile because of a problem with line 2. What s the problem? public String met( String [] a ){ String x = a.substring( 0, 1 ); return x; Page 3

4 27. If the array is { "dog", "two fish" what is displayed? 28. What is displayed? Write your answers in the spaces provided. public void met( String [] a ){ System.out.println( a[0].length() ); System.out.println( a.length ); public class Word { private String [] ltrs; public class Runner { public static void main(string[] args) { Word w = new Word( "pony" ); w.change( 2, 3 ); w.change( 3, 0 ); public Word( String s ) { ltrs = new String[ s.length() ]; for ( int n = 0; n < ltrs.length; n++ ) ltrs[n] = s.substring( n, n+1 ); public void change( int n1, int n2 ) { String temp = ltrs[ n1 ]; ltrs[ n1 ] = ltrs[ n2 ]; ltrs[ n2 ] = temp; public String tostring() { String temp = ""; for ( int n = 0; n < ltrs.length; n++ ) temp += ltrs[n]; return temp; 29. What is the first line of the Toy constructor? 30. What is the first line of the open method? 31. What is the first line of the get method? Toy [] t = new Toy[ 4 ]; for ( int n = 0; n < 4; n++ ){ t[n] = new Toy( true ); t[n].open( 12 ); double x = t[n].get(); 32. What is the first line of the Ax constructor? public 33. What is the first line of the get method? public int n = (int)(10*math.random())+ 3; Ax [] a = new Ax[ n ]; for ( int i = 0; i < a.length; i++ ){ a[i] = new Ax(); if ( a[i].get() > 10 ) System.out.println( "!!!" ); Page 4

5 Problems 34 to 37 refer to the Rectangle class defined below to the right. 34. What does the following statement do? Rectangle [] r1; a) It creates a variable that can hold a reference to an array of Rectangles. b) Same as (a) but it also creates an array object. public class Rectangle{ private int width, length; public Rectangle( int w, int len ){ width = w; length = len; 35. What does the following statement do? Rectangle [] r2 = new Rectangle[5]; a) It creates a variable and five Rectangle objects. b) It creates a variable, an array object, and five Rectangle objects. c) It creates a variable and an array object. It creates no Rectangle objects. public int area(){ return width*length; public void setwidth( int w ){ width = w; public String tostring(){ return length + ", " + width; 36. This compiles and runs. What does it display? 37. This compiles and runs. What does it display? public class Runner1{ public static void main( String[] args ){ Rectangle[] r = new Rectangle[3]; r[0] = new Rectangle( 3, 2 ); r[1] = new Rectangle( 5, 1 ); r[2] = new Rectangle( 2, 6 ); int tot = 0; for ( int i = 0; i < r.length; i++ ) tot += r[i].area(); System.out.println( tot ); r[1].setwidth( 4 ); for ( int i = 0; i < r.length; i++ ) System.out.println( r[i].tostring() ); public class Runner2{ public static void main( String[] args ){ Rectangle[] ray = new Rectangle[5]; for ( int i = 0; i < ray.length; i++ ){ ray[i] = new Rectangle( i+1, i+1 ); System.out.println( ray[i].area() ); Page 5