Writing Functions - Laboratory 4 - Fall 2008 | CS 1110 | Lab Reports Computer Science

CS1110 Lab 04. Writing functions Fall 2008

Name _____________________ NetId __________

Section time _______________ Section instructor ___________________

The purpose of this lab is to give you practice with developing the bodies of methods. At the same time, this

lab will give you practice with Strings. This lab will help you prepare for the prelim. We begin with some

information on Strings. We also introduce you to the equality comparison operator == and its counterpart,

function equals. After this lab, study Section 5.2 of the text, beginning on page 175.

A String object (instance, or folder) associates a number with each character in its list. The number is

called the index or position of the character. Type the following line into the interactions pane of Dr. Java:

String s= "Java is fun.";

String object s now contains the list of characters "Java is fun.". The index of each character is shown

below:

index 0 1 2 3 4 5 6 7 8 9 10 11

s J a v a i s f u n .

The index of the first character is 0 (not 1), and the space character between each of the words and the

period each have an index.

In the string "I will study every day.", what is the index of the character 'w'? How about the last

space character? Write down your answers:

A list of some functions that appear in each String object (there are more, which you can find in the

specification of class String in the API package) is given at the end of this handout. Refer to it when doing

this lab. Note also that if a string s contains only digits (not even blanks), then the function call

Integer.parseInt(s)

yields the integer represented by s. For example, Integer.parseInt("345") is 345.

Important point about Equality

Symbol ==code> is used for equality testing. You know that 2+3 == 5 is true. However, when x and y are

of the same class -type, the test x == y is made on the names of the folders. Therefore:

new C(args) == new C(args) is always false because two folders, with different names,

are created.

Evaluate the following expressions in the interactions pane and write down their values. In the third one, for

each occurrence of "ab", evaluation in the interactions pane creates a new manilla folder of class String.

new String("ab") == new String("ab") value:

new Integer(5) == new Integer(5) value:

"ab" == "ab" value:

Method Object, the superest class of them all has a boolean function equals(Object), which in class

Partial preview of the text

Download Writing Functions - Laboratory 4 - Fall 2008 | CS 1110 and more Lab Reports Computer Science in PDF only on Docsity!

CS1110 Lab 04. Writing functions Fall 2008

Name _____________________ NetId __________ Section time _______________ Section instructor ___________________ The purpose of this lab is to give you practice with developing the bodies of methods. At the same time, this lab will give you practice with Strings. This lab will help you prepare for the prelim. We begin with some information on Strings. We also introduce you to the equality comparison operator == and its counterpart, function equals. After this lab, study Section 5.2 of the text, beginning on page 175. A String object (instance, or folder) associates a number with each character in its list. The number is called the index or position of the character. Type the following line into the interactions pane of Dr. Java: String s= "Java is fun."; String object s now contains the list of characters "Java is fun.". The index of each character is shown below: index 0 1 2 3 4 5 6 7 8 9 10 11 s J a v a i s f u n. The index of the first character is 0 (not 1), and the space character between each of the words and the period each have an index. In the string "I will study every day.", what is the index of the character 'w'? How about the last space character? Write down your answers: A list of some functions that appear in each String object (there are more, which you can find in the specification of class String in the API package) is given at the end of this handout. Refer to it when doing this lab. Note also that if a string s contains only digits (not even blanks), then the function call Integer.parseInt(s) yields the integer represented by s. For example, Integer.parseInt("345") is 345. Important point about Equality Symbol ==code> is used for equality testing. You know that 2+3 == 5 is true. However, when x and y are of the same class-type, the test x == y is made on the names of the folders. Therefore: new C(args) == new C(args) is always false because two folders, with different names, are created. Evaluate the following expressions in the interactions pane and write down their values. In the third one, for each occurrence of "ab", evaluation in the interactions pane creates a new manilla folder of class String. new String("ab") == new String("ab") value: new Integer(5) == new Integer(5) value: "ab" == "ab" value: Method Object, the superest class of them all has a boolean function equals(Object), which in class

Object is defined to work exactly like ==. Therefore, each class can override function equals, and the convention is to define equals to test for the equality of all the fields in two objects. For example, classes String and Integer override this method. To see this, try the following in the interactions pane and write down their values: (new String("ab")).equals("ab") value: (new Integer(5)).equals(new Integer(5)) value: "ab".equals("ab") value: You need to understand this distinction between == and function equals for the first prelim. Read about equality of strings on page 179 and equality testing on page 118. WRITING METHODS THAT DEAL WITH STRINGS Below, we specify a bunch of methods for you to write. Do as many of them as you can in this lab. You probably won't finish them. We hope that you will finish THREE of them during the lab —show them to your lab instructor at the end of the lab. How much of the others you do is up to you. The more you practice, the easier developing such programs will become. The methods will, among other things, change a time in a String into a different format. The time comes in four formats: 24-hour-string: ":" is in range 0:23 and is in range 0.. Examples: "4:20" "13:00" "23:59" AM-PM-string: ":AM" or ":PM" is in range 0:11 and is in range 0.. Examples: "4:20AM" "3:00PM" "11:59PM" "0:0" 24-hour-verbose Example: "4 hours and 20 minutes" Example: "23 hours and 5 minutes" Note: exactly one blank between each of the pieces. 24-hour-correct Exactly like the 24-hour-verbose format except that it is gramatically correct. So, instead of "1 hours and 20 minutes" it reads "1 hour and 20 minutes" and instead of "0 hours and 1 minutes" it reads "0 hours and 1 minute". What to do When you are finished writing and testing (THREE of) the functions given below, show them to your lab instructor. We suggest that you save both .java files that you created on a USB storage key or else email them to yourself. If you do not have time to finish three in the allotted time, then show the completed lab to your instructor the next week. First , create in DrJava a new class Methods and save it appropriately — remember, put all files for a new program in a new folder. To simplify your work, you can download file Methods.java from here or from the course website; it has all the methods in it already. The function bodies have return statements so that the class will compile. Second , create a JUnit test class, as usual.

Return the time as the number of minutes. E.g. "14:35" is 1460 + 35. See if you can write the body as a single return statement. / public static int AMPMtimeInMinutes(String s) { return 0; } / = time s1 < time s2; Precondition: s1 and s2 are in either 24-hour-string format or AM-PM-string format See if you can write the body as a single return statement. */ public static boolean isLess(String s1, String s2) return false; } s.length() = the length of s —the number of characters in it. Can be 0. "abc".length() is 3 s.charAt(i) = the character at index i of String s, which we might write as s[i]. The result is of type char. "abc".charAt(1) is 'b' s.substring(b,e) = the String s[b..e–1] —consists of chars s[b], s[b+1], ..., b[e–1]. "abc".substring(1,3) is "bc" s.substring(b) (^) = the String s[b..], or s[b..s.length()–1]. "abc".substring(1) is "bc" s.indexOf(s1) = the index of the first char of the FIRST occurrence of String s1 in s (–1 if s does not occur in s). "abbc".indexOf("b") is 1 s.indexOf(c) = the index of the FIRST occurrence of character c in s (–1 if s1 does not occur in s ). "abbc".indexOf('b') is 1 s.lastIndexOf(s1) = the index of the first char of the LAST occurrence of String s1 in s (–1 if s does not occur in s). "abbc".lastIndexOf("b") is 2 s.trim() = s with preceding and ending whitespace removed. " abbc ".trim() is "abbc" s.startsWith(s1) = "s begins with String s1", i.e. = true if s begins with s1 and false otherwise "abbc".startsWith("b") is false s.endsWith(s1) (^) = "s ends with String s1". "abbc".endsWith("c") is true s.equals(s1) = true if s and s1 contains the same sequences of characters, i.e. the same strings. "abbc".equals("abbc") is true "abbc".equals("abbcd") is false s.compareTo(s1) = negative, 0 , or positive, depending on whether s is less than, equal to, or greater than s1. The comparison is based on alphabetic ordering, as in the dictionary. "abbc".compareTo("a") is 3 "abbc".compareTo("abbcdb") is –

Writing Functions - Laboratory 4 - Fall 2008 | CS 1110, Lab Reports of Computer Science

Related documents

Partial preview of the text

Download Writing Functions - Laboratory 4 - Fall 2008 | CS 1110 and more Lab Reports Computer Science in PDF only on Docsity!

CS1110 Lab 04. Writing functions Fall 2008