1. Lecture 10
Strings
CSE 1322
4/26/2018

2. String class
A string is a sequence of characters stored in a certain address in memory.
Once created, it cannot be changed. It is an immutable object because the string class has no mutators methods.
Unlike other objects, it does not need to be explicitly instantiated
After being assigned once, the content of the variable does not change directly – if we try to change the value, it will be saved to a new location in the dynamic memory and the variable will point to it.
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3. Strings java Strings are objects of the String class
String constants or literals:
String variables:
String length:
Empty string:
"Hello, World!"
String message = "Hello, World!";
int n = message.length();
""
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4. Strings C# Strings are objects of the string class
String constants or literals:
String variables:
String length:
Empty string:
"Hello, World!"
string message = "Hello, World!";
int n = message.Length;
""
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5. String Object vs String Reference
String Constant Pool
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6. String Object vs String Reference
String Constant Pool
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7. Concatenation Use the + operator:
If one of the arguments of the + operator is a string, the other is converted to a string
String name = "Dave"; String message = "Hello, " + name; // message is "Hello, Dave"
String a = "Agent"; int n = 7; String bond = a + n; // bond is Agent7
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8. Concatenation Use the + operator:
If one of the arguments of the + operator is a string, the other is converted to a string
string name = "Dave"; string message = "Hello, " + name; // message is "Hello, Dave"
string a = "Agent"; int n = 7; String bond = a + n; // bond is Agent7
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9. Concatenation in Print Statements
Useful to reduce the number of System.out.print instructions
versus
System.out.print("The total is "); System.out.println(total);
System.out.println("The total is " + total);
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10. Concatenation in Print Statements
Useful to reduce the number of Console.Write instructions
versus
Console.Write("The total is "); Console.WriteLIne(total);
Console.WriteLine("The total is " + total);
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11. Converting between Strings and Numbers
Convert to number:
Convert to string:
int n = Integer.parseInt(str); double x = Double.parseDouble(x);
String str = "" + n; str = Integer.toString(n);
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12. Converting between Strings and Numbers
Convert to number:
Convert to string:
int n = int.ParseInt(str); double x = double.Parse(x);
String str = "" + n; int many = 5;
string xyz = many.ToString();
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13. Substrings Java Supply start and “past the end” position
String greeting = "Hello, World!"; String sub = greeting.substring(0, 5);
// sub is "Hello"
Supply start and “past the end” position
First position is at 0
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14. Substrings Java Substring length is “past the end” - start
String greeting = "Hello, World!"; String sub = greeting.substring(7, 12);
// sub is “World"
Substring length is “past the end” - start
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15. Substrings C# Supply start and the number of characters desired
string greeting = "Hello, World!"; string sub = greeting.substring(0, 5);
// sub is "Hello"
Supply start and the number of characters desired
First position is at 0
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16. Substrings Java
String greeting = "Hello, World!"; String sub = greeting.substring(7, 12);
// sub is “World"
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17. Challenge String s ="Agent“;
What is the effect of the assignment s = s + s.length()?
String river ="Mississippi“:
what is the value of river.substring(1, 2)?
what is the value of river.substring(2, river.length() - 3)?
What is the value of river.substring(1)?
string s ="Agent“;
What is the effect of the assignment s = s + s.Length;
string river ="Mississippi“:
what is the value of river.Substring(1, 2)?
what is the value of river.Substring(2, river.Length- 3)?
What is the value of river.Substring(1)?
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18. Answers Agent5 i ssiss ississippi Agent5 i ssissip ississippi
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19. 4/26/2018

20. Length Property
public int Length { get; } The number of characters in the current string. Remarks The Length property returns the number of Char objects in this instance, not the number of Unicode characters. Example: string h= “hello”; int len = h.Length; len has a value of 5
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21. To upper and lower case
public string ToLower() Return Value: A string in lowercase. public string ToUpper() Return Value: A string in uppercase. Example: string myString = “good luck”; myString = myString.ToUpper(); myString now has the value “GOOD LUCK”
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22. To upper and lower case
public string ToLower() Return Value: A string in lowercase. public string ToUpper() Return Value: A string in uppercase. Example: string myString = “good luck”; myString = myString.ToUpper(); myString now has the value “GOOD LUCK”
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23. To upper and lower case
public string toLowerCase() Return Value: A string in lowercase. public string toUpperCase() Return Value: A string in uppercase. Example: String myString = “good luck”; myString = myString.toUpperCase(); myString now has the value “GOOD LUCK”
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24. IndexOf methods
public int IndexOf( char value ) The zero-based index position of value if that character is found, or -1 if it is not. public int IndexOf( string value) The zero-based index position of value if that string is found, or -1 if it is not. string myString= “hello world”; int e_index=myString.IndexOf(‘e’); // e_index= 1 int or_index= myString.IndexOf(“or”); //or_index=7
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25. indexOf methods
public int indexOf( char value ) The zero-based index position of value if that character is found, or -1 if it is not. public int indexOf( string value) The zero-based index position of value if that string is found, or -1 if it is not. String myString= “hello world”; int e_index=myString.indexOf(‘e’); // e_index= 1 int or_index= myString.indexOf(“or”); //or_index=7
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26. Problem-1: Reverse a String (Using a Char Array)
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27. Problem-1: Reverse a String (in place)
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28. Problem-1: Reverse a String (in place)
public class StringReverseInPlaceEx1 {
public static void main(String[] args) {
String a = “INFORMATION";
System.out.println(reverse(a)); //NOITAMROFNI }
private static String reverse(String a) {
char[] ca = a.toCharArray();
int start = 0 ; int end = a.length()-1;
while(end > start) {
swap(ca,start,end);
start++; end--;
}//while
return new String(ca);
private static void swap(char[] ca, int start, int end) {
char t = ca[start];
ca[start] = ca[end]; ca[end] = t ;
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29. Problem-1: Reverse a String (in place)
public class StringReverseInPlaceEx2 {
public static void main(String[] args) {
String a = "INFORMATION";
System.out.println(StringReverseInPlace(a)); //NOITAMROFNI }
public static String StringReverseInPlace(String toReverse) {
char[] chars = toReverse.toCharArray();
int inputStringLength = toReverse.length();
for (int i = 0; i < inputStringLength / 2; i++) {
int toMoveBack = toReverse.charAt(i);
int toMoveForward = toReverse.charAt(inputStringLength - i - 1);
//swap
toMoveForward = toMoveBack - toMoveForward;
toMoveBack -= toMoveForward;
toMoveForward += toMoveBack;
chars[i] = (char) toMoveBack;
chars[inputStringLength - i - 1] = (char) toMoveForward;
return String.valueOf(chars);
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30. Null Initialization vs Empty String
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31. Frequently Used String Methods
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