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Chapter 16 Slides

Exposure Java. Chapter 16 Slides. String Classes and Methods. PowerPoint Presentation created by: Mr. John L. M. Schram. From Materials Created by Mr. Leon Schram. String Definition. A string is a set of characters that behaves as a single unit.

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Chapter 16 Slides

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  1. Exposure Java Chapter 16 Slides String Classes and Methods PowerPoint Presentation created by: Mr. John L. M. Schram From Materials Created by Mr. Leon Schram

  2. String Definition • A string is a set of characters that behaves as a single • unit. • The characters in a string include upper-case and lower-case letters, numerical characters and a large set of characters for a variety of purposes like: • ! @ # $ % ^ & * ( ) _ +

  3. String Literal Definition A string literal is a set of characters delimited with double quotations like: "Seymour Snodgrass" and "SSN: 123-45-6789"

  4. // Java1601.java // This program demonstrates how to declare five String objects. // Note that all five string objects store the same information. public class Java1601 { public static void main (String args[]) { String s1 = "Tango"; System.out.println("s1: " + s1); String s2; s2 = "Tango"; System.out.println("s2: " + s2); String s3 = new String("Tango"); System.out.println("s3: " + s3); String s4 = new String(); s4 = "Tango"; System.out.println("s4: " + s4); char Dance[] = {'T','a','n','g','o'}; String s5 = new String(Dance); System.out.println("s5: " + s5); System.out.println(); } } Java1601.java Output s1: Tango s2: Tango s3: Tango s4: Tango s5: Tango

  5. Mathematical Addition 100 + 200 = 300 int x = 100; x += 200;

  6. String Concatenation “100” + “200” = “100200” String x = “100”; x += “200”;

  7. // Java1602.java // This program shows how to concatenate strings using the // + operator and the <concat> method. public class Java1602 { public static void main (String args[]) { String s1 = "Argentine"; String s2 = "Tango"; String s3 = s1 + " " + s2; System.out.println("s3: " + s3); String s4 = "Argentine"; s4 = s4.concat(" Tango"); System.out.println("s4: " + s4); System.out.println(); } } Java1602.java Output s3: Argentine Tango s4: Argentine Tango

  8. String method concat s1 = s2.concat("hiss"); concat concatenates the method argument to the object string. If s2 =="boo" then s1 will become "boohiss"

  9. // Java1603.java // This program demonstrates the use of the <length> method. public class Java1603 { public static void main (String args[]) { String s1 = "Argentine"; String s2 = "Tango"; String s3 = s1 + " " + s2; System.out.println(s1 + " has " + s1.length() + " characters."); System.out.println(s2 + " has " + s2.length() + " characters."); System.out.println(s3 + " has " + s3.length() + " characters."); System.out.println(); } } Java1603.java Output Argentine has 9 characters. Tango has 5 characters. Argentine Tango has 15 characters.

  10. // Java1604.java // This program demonstrates how to access individual characters of // a String object with the <charAt> method. public class Java1604 { public static void main (String args[]) { String s1 = "Madam I'm Adam"; String s2 = ""; int N = s1.length() - 1; for (int K = N; K >= 0; K--) s2 += s1.charAt(K); System.out.println("s1: " + s1); System.out.println("s2: " + s2); System.out.println(); } } Java1604.java Output s1: Madam I'm Adam s2: madA m'I madaM

  11. String method charAt letter = s.charAt(k); Method charAt returns the character stored at the kth index location of the string object s. The first character is at index 0. If s == "Aardvark" and k == 4 then letter becomes v

  12. // Java1605.java // This program demonstrates how to access specified characters of // a string with the <substring(SI,EI)> method, where SI is the StartIndex // and EI is one less than the EndIndex. public class Java1605 { public static void main (String args[]) { String s = "Racecar"; int n = s.length(); for (int k = 1; k <= n; k++) System.out.println(s.substring(0,k)); System.out.println(); for (int k = 0; k <= n-3; k++) System.out.println(s.substring(k,k+3)); System.out.println(); } } Java1605.java Output R Ra Rac Race Racec Raceca Racecar Rac ace cec eca car

  13. String method substring s2 = s1.substring(0,k); Method substring returns a set of consecutive characters from string s1, starting at index 0, and ending at index k-1. If s1 == "Aardvark"and k == 4 then s2 becomes "Aard"

  14. // Java1606.java // This program shows the <indexOf> method, which returns the index of the // first occurrence of the string argument, and the <lastIndexOf> method, which returns the // index of the last occurrence of the string argument. public class Java1606 { public static void main (String args[]) { String s1 = "racecar"; String s2 = "racecar in the carport"; String s3 = "car"; int index1 = s1.indexOf(s3); int index2 = s1.lastIndexOf(s3); int index3 = s2.indexOf(s3); int index4 = s2.lastIndexOf(s3); int index5 = s1.indexOf("qwerty"); System.out.println("With \"" + s1 + "\" car starts at " + index1 + " and last shows up at " + index2); System.out.println("With \"" + s2 + "\" car starts at " + index3 + " and last shows up at " + index4); System.out.println("With \"" + s3 + "\" Qwerty shows up at " + index5); System.out.println(); } } Java1606.java Output With "racecar" car starts at 4 and last shows up at 4 With "racecar in the carport" car starts at 4 and last shows up at 15 With "racecar" Qwerty shows up at -1

  15. // Java1607.java // This program demonstrates the <replace(Old,New)> String // method, which replaces all occurrences of the Old character // with the New character. // This method creates a new String object with the replaced characters. public class Java1607 { public static void main (String args[]) { String s1 = "racecar"; String s2 = s1.replace('r','l'); System.out.println("s1: " + s1); System.out.println("s2: " + s2); System.out.println(); } } Java1607.java Output s1: racecar s2: lacecal

  16. String method replace String s2 = s1.replace('m','b'); Method replace returns a string such that every occurrence of the Old character ('m') is replaced by the New character ('b') . If s1 == "madam" then s becomes "badab”

  17. // Java1608.java // This program demonstrates the String <toUpperCase> and // <toLowerCase> methods. public class Java1608 { public static void main (String args[]) { String s1 = "racecar"; String s2 = "RaCeCaR"; String s3 = "RACECAR100"; String s4 = s1.toUpperCase(); String s5 = s2.toUpperCase(); String s6 = s3.toUpperCase(); System.out.println("s1 --> s4: " + s4); System.out.println("s2 --> s5: " + s5); System.out.println("s3 --> s6: " + s6); System.out.println(); s1 = s4.toLowerCase(); s2 = s5.toLowerCase(); s3 = s6.toLowerCase(); System.out.println("s4 --> s1: " + s1); System.out.println("s5 --> s2: " + s2); System.out.println("s6 --> s3: " + s3); System.out.println(); } } Java1608.java Output s1 --> s4: RACECAR s2 --> s5: RACECAR s3 --> s6: RACECAR100 s4 --> s1: racecar s5 --> s2: racecar s6 --> s3: racecar100

  18. String methods toUpperCaseand toLowerCase s1 = s2.toLowerCase; s3 = s1.toUpperCase; Method toLowerCase returns a string with lower-case letters. Method toUpperCase returns a string with upper-case letters. Any characters that are not letters will be ignored by both methods and returned in their same relative string position.

  19. // Java1609.java // This program demonstrates the <valueOf> method of the String class, // which is shown to convert four data types to a string. // Note that <valueOf> is a static method and must be called using <String.valueOf>. public class Java1609 { public static void main (String args[]) { String s1 = String.valueOf(1000); String s2 = String.valueOf(123.321); String s3 = String.valueOf(true); String s4 = String.valueOf('A'); System.out.println("s1: " + s1); System.out.println("s2: " + s2); System.out.println("s3: " + s3); System.out.println("s4: " + s4); System.out.println(); } } Java1609.java Output s1: 1000 s2: 123.321 s3: true s4: A

  20. String static method valueOf String s1 = String.valueOf(1000); String s2 = String.valueOf(123.321); String s3 = String.valueOf(true); String s4 = String.valueOf('A'); Method valueOf converts the provided parameter and returns a string. Four overloaded valueOf methods are displayed. Note that the valueOf method is a static method that is called with the String class identifier.

  21. Integer methods parseInt and parseDouble int n1 = Integer.parseInt(s1); double n2 = Double.parseDouble(s2); Method parseInt converts a string into an integer. Method parseDouble converts a string into a double. Parameters that include non-numerical characters will compile, but will cause a run-time error.

  22. // Java1610.java // This program converts string values to integer and double values // using the <parseInt> and <parseDouble> methods of the <Integer> // and <Double> classes. public class Java1610 { public static void main (String args[]) { String s1 = "12345"; String s2 = "123.321"; int n1 = Integer.parseInt(s1); double n2 = Double.parseDouble(s2); System.out.println(n1 + " + " + n1 + " = " + (n1 + n1)); System.out.println(n2 + " + " + n2 + " = " + (n2 + n2)); System.out.println(); } } Java1610.java Output 12345 + 12345 = 24690 123.321 + 123.321 = 246.642

  23. // Java1611.java // This program checks the equality of two strings with the == operator. // The program executes as you might expect. public class Java1611 { public static void main (String args[]) { String s1 = "Foxtrot"; String s2 = "Waltz"; String s3 = "Foxtrot"; if (s1 == s2) System.out.println(s1 + " == " + s2); else System.out.println(s1 + " != " + s2); if (s1 == s3) System.out.println(s1 + " == " + s3); else System.out.println(s1 + " != " + s3); System.out.println(); } } Java1611.java Output Foxtrot != Waltz Foxtrot == Foxtrot

  24. // Java1612.java // This program checks equality of strings, but this time a string entered at the keyboard // is used for comparison. This program has unexpected results. import java.io.*; public class Java1612 { public static void main (String args[]) throws IOException { BufferedReader input = new BufferedReader(new InputStreamReader(System.in)); String s1 = "Foxtrot"; String s2 = "Waltz"; System.out.print("Enter a string ===>> "); String s3 = input.readLine(); if (s1 == s2) System.out.println(s1 + " == " + s2); else System.out.println(s1 + " != " + s2); if (s1 == s3) System.out.println(s1 + " == " + s3); else System.out.println(s1 + " != " + s3); System.out.println(); } } Java1612.java Output Enter a string ===>> Foxtrot Foxtrot != Waltz Foxtrot != Foxtrot

  25. // Java1613.java // This program uses the <trim> method, which removes "white space" from both ends of the // string argument. This method is used to try and solve the problem of the previous program. import java.io.*; public class Java1613 { public static void main (String args[]) throws IOException { BufferedReader input = new BufferedReader(new InputStreamReader(System.in)); String s1 = "Foxtrot"; String s2 = "Waltz"; System.out.print("Enter a string ===>> "); String s3 = input.readLine(); if (s1 == s2) System.out.println(s1 + " == " + s2); else System.out.println(s1 + " != " + s2); if (s1 == s3.trim()) System.out.println(s1 + " == " + s3); else System.out.println(s1 + " != " + s3); System.out.println(); } } Java1613.java Output Enter a string ===>> Foxtrot Foxtrot != Waltz Foxtrot != Foxtrot

  26. String method trim s1 = s2.trim(); String method trim returns a string with "white space" removed from both ends of the String object.

  27. // Java1614.java // This program demonstrates the <equals> method, which is capable of // testing equality of string objects correctly.import java.io.*; public class Java1614 { public static void main (String args[]) throws IOException { BufferedReader input = new BufferedReader(new InputStreamReader(System.in)); String s1 = "Foxtrot"; String s2 = "Waltz"; System.out.print("Enter a string ===>> "); String s3 = input.readLine(); if (s1.equals(s2)) System.out.println(s1 + " == " + s2); else System.out.println(s1 + " != " + s2); if (s1.equals(s3)) System.out.println(s1 + " == " + s3); else System.out.println(s1 + " != " + s3); System.out.println(); } } Java1614.java Output Enter a string ===>> Foxtrot Foxtrot != Waltz Foxtrot == Foxtrot

  28. What is going on? Figure 16.19 shows that s1 and s3 both reference a memory location where the value "Foxtrot" is stored, but the values of s1 and s3 are not equal.

  29. // Java1615.java // This program demonstrates the <compareTo> method, which returns an integer value. // The value is 0 when the strings are equal, otherwise a value is returned that // indicates the relative distance between the strings. public class Java1615 { public static void main (String args[]) { String s1 = "AARDVARK"; String s2 = "ZEBRA"; String s3 = "AARDVARK"; String s4 = "BART"; int value1 = s1.compareTo(s2); int value2 = s1.compareTo(s3); int value3 = s2.compareTo(s1); int value4 = s1.compareTo(s4); System.out.println("value1: " + value1); System.out.println("value2: " + value2); System.out.println("value3: " + value3); System.out.println("value4: " + value4); System.out.println(); } } Java1615.java Output Value1: -25 Value2: 0 Value3: 25 Value4: -1

  30. String methodsequals and compareTo if (s1.equals(s2)) int distance = s3.compareTo(s4); Method equals returns true is s1 == s2, and false otherwise. Method compareTo returns 0 if s3 == s4, otherwise an integer is returned based on the difference between s3 and s4. If s3 < s4, the returned value is negative.

  31. String Objects are Immutable • A mutator is a method that mutates or alters object values. The character contents of a string object cannot be altered, which means that string objects are immutable. • You need to construct a StringBuffer object if it is necessary to change the character content after the object is constructed.

  32. // Java1616.java // This program introduces the <StringBuffer> class. // Three different approaches are shown to construct a StringBuffer object. // You cannot assign a String to a StringBuffer object. class Java1616 { public static void main (String args[]) { // constructs a StringBuffer object with capacity 16 and no characters StringBuffer s1 = new StringBuffer(); // s1 = "This will not compile"; System.out.println("s1: " + s1); // constructs a StringBuffer object with capacity 50 and no characters StringBuffer s2 = new StringBuffer(50); System.out.println("s2: " + s2); // constructs a StringBuffer object with required capacity and stores the string argument StringBuffer s3 = new StringBuffer("The quick brown fox jumps over the lazy dog"); System.out.println("s3: " + s3); System.out.println(); } } Java1616.java (with comment removed) Output Java1616.java:12: incompatible types found : java.lang.String required: java.lang.StringBuffer s1 = "This won't work"; ^ 1 error Java1616.java Output s1: s2: s3: The quick brown fox jumps over the lazy dog

  33. // Java1617.java // This program demonstrates the <insert> method, which inserts a new string at a // specified location. // The <insert> method automatically allocates the required StringBuffer space. public class Java1617 { public static void main (String args[]) { StringBuffer s1 = new StringBuffer(); s1.insert(0,"The quick brown fox jumps over the lazy dog"); System.out.println("s1: " + s1); StringBuffer s2 = new StringBuffer(50); s2.insert(0,"The quick brown fox jumps over the lazy dog"); System.out.println("s2: " + s2); StringBuffer s3 = new StringBuffer("The quick brown fox jumps over the lazy dog"); s3.insert(4,"ever so "); System.out.println("s3: " + s3); System.out.println(); } } Java1617.java Output s1: The quick brown fox jumps over the lazy dog s2: The quick brown fox jumps over the lazy dog s3: The ever so quick brown fox jumps over the lazy dog

  34. StringBuffer insert method s.insert(index,newString); Method insert adds newString to the existing StringBuffer object s, at the index character location.

  35. // Java1618.java // This program demonstrates the <length>, <capacity> and <setLength> methods. // Length returns the size of the stored string. Capacity returns the size of the StringBuffer, // and setLength alters the size of the stringBuffer. // Note how 16 extra spaces are constructed with a string argument construction. public class Java1618 { public static void main (String args[]) { StringBuffer s1 = new StringBuffer(); System.out.println("Length: " + s1.length()); System.out.println("Capacity: " + s1.capacity()); s1.insert(0,"The quick brown fox jumps over the lazy dog"); System.out.println("Length: " + s1.length()); System.out.println("Capacity: " + s1.capacity()); System.out.println(); StringBuffer s2 = new StringBuffer(50); System.out.println("Length: " + s2.length()); System.out.println("Capacity: " + s2.capacity()); s2.insert(0,"The quick brown fox jumps over the lazy dog"); System.out.println("Length: " + s2.length()); System.out.println("Capacity: " + s2.capacity()); System.out.println(); StringBuffer s3 = new StringBuffer("The quick brown fox jumps over the lazy dog"); System.out.println("Length: " + s3.length()); System.out.println("Capacity: " + s3.capacity()); s3.insert(4,"ever so "); System.out.println("Length: " + s3.length()); System.out.println("Capacity: " + s3.capacity()); System.out.println(); s1.setLength(1000); System.out.println("Length: " + s1.length()); System.out.println("Capacity: " + s1.capacity()); } } Java1618.java Output Length: 0 Capacity: 16 Length: 43 Capacity: 43 Length: 0 Capacity: 50 Length: 43 Capacity: 50 Length: 43 Capacity: 59 Length: 51 Capacity: 59 Length: 1000 Capacity: 1000 Try This! Display the value of s1 at the end of the program.

  36. length, capacity and setLength int len = s.length(); int cap = s.capacity(); s.setLength(1000); Method length returns the size of the StringBuffer object. Method capacity returns buffer capacity for total characters. Method setLength sets the size of the StringBuffer object and appends the string with null characters.

  37. // Java1619.java // This program demonstrates how to use the <charAt> method to // access individual characters in a StringBuffer object. public class Java1619 { public static void main (String args[]) { StringBuffer s1 = new StringBuffer( "Madam I'm Adam"); StringBuffer s2 = new StringBuffer(100); int n = s1.length(); for (int k = 0; k < n; k++) s2.insert(k, s1.charAt(n-k-1)); System.out.println("s1: " + s1); System.out.println("s2: " + s2); System.out.println(); } } Java1619.java Output s1: Madam I'm Adam s2: madA m'I madaM

  38. // Java1620.java // This program demonstrates how the <setCharAt> method replaces // characters in a StringBuffer object. public class Java1620 { public static void main (String args[]) { StringBuffer s = new StringBuffer( "Aardvark"); System.out.println(s); s.setCharAt(0,'E'); s.setCharAt(1,'e'); s.setCharAt(5,'e'); System.out.println(s); System.out.println(); } } Java1620.java Output Aardvark Eerdverk

  39. StringBuffer setCharAt method s.setCharAt(5,'A'); Method setCharAt replaces the character at index 5 of the s object with character 'A'.

  40. // Java1621.java // This program demonstrates the <delete(SI,EI)> method, which deletes a substring // from a StringBuffer object from StartingIndex to EndIndex-1. public class Java1621 { public static void main (String args[]) { StringBuffer s = new StringBuffer( "The quick brown fox jumps over the lazy dog"); System.out.println(s); s.delete(9,15); System.out.println(s); s.delete(3,9); System.out.println(s); System.out.println(); } } Java1621.java Output The quick brown fox jumps over the lazy dog The quick fox jumps over the lazy dog The fox jumps over the lazy dog

  41. StringBuffer delete method s.delete(4,7); Method delete removes a substring from s starting at index 4 and ending at index 6. If s == "Discombobulated" then after the s.delete(4,7); call s becomes "Discobulated".

  42. // Java1622.java // This program demonstrates the <replace(SI,EI,S)> method, which replaces a substring // from a StringBuffer object from StartingIndex to EndIndex-1 with string S. public class Java1622 { public static void main (String args[]) { StringBuffer s = new StringBuffer( "The quick brown fox jumps over the lazy dog"); System.out.println(s); s.replace(10,15,"red"); System.out.println(s); s.replace(4,9,"slow"); System.out.println(s); System.out.println(); } } Java1620.java Output The quick brown fox jumps over the lazy dog The quick red fox jumps over the lazy dog The slow red fox jumps over the lazy dog

  43. StringBuffer replace method s.replace(0,3,"lear"); Method replace deletes a substring of s from start index 0 to last index 2, and replaces this space with "lear". If s == "burning" then after replace, s == "learning"

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