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Java Strings

Slides provided by the University of Washington Computer Science & Engineering department.

Strings

• string: an object storing a sequence of text characters.
• Creating a string:

String name = "text"; String name = expression;

• Examples:

String name = "Marty Stepp"; int x = 3; int y = 5; String point = "(" + x + ", " + y + ")";

String indexes

• Characters of a string are numbered with 0-based indexes:

String fruit = "Apple";

• First character’s index: 0
• Last character’s index: 1 less than the string’s length

index

1 2 3 4

character

A p p l e

String methods

Method name Description int length() number of characters in this string String substring(int from, int to) returns the substring beginning at from and ending at to-1 String substring(int from) returns substring(from, length()) int indexOf(String str) returns the index of the first occurrence of str; returns -1 if not found int compareTo(String other) returns a value < 0 if this is less than other returns a value = 0 if this is equal to other returns a value > 0 if this is greater than other

String methods

• These methods are called using the dot notation:

String veggie = "carrot"; System.out.println(veggie.length()); // 6

• More examples:

// index 012345678901 String s1 = "Stuart Reges"; System.out.println(s1.length()); // 12 System.out.println(s1.indexOf("e")); // 8 System.out.println(s1.substring(7, 10)); // "Reg"

String methods

• Given the following string:

String message = "Hello, world!";

• How would you extract the word “world”?

The equals method

• Objects are compared using a method named equals.

if (string1.equals(string2)) { System.out.println("The strings are equal!"); }

• Technically this is a method that returns a value of type boolean, the type

used in logical tests.

String question

Write a static method numWords that takes a String as a parameter and that returns the number of words in the

• String. By definition, words are separated by one or

more spaces.

numWords("how many?")

Returns 2

numWords(" how about a-b-c and !&%-$!*() ")

Returns 5 PROBLEM: EXAMPLES:

numWords solution 1

public static int numWords(String s) { int count = 0; boolean insideWord = false; for (int i = 0; i < s.length(); i++) { String current = s.substring(i, i + 1); if (current.equals(" ")) { insideWord = false; } else if (!insideWord) { count++; insideWord = true; } } return count; }

• Here’s one way to solve the problem:

numWords solution 2

public static int numWords(String s) { int count = 0; String prev = " "; for (int i = 0; i < s.length(); i++) { String current = s.substring(i, i + 1); if (prev.equals(" ") && !current.equals(" ")) { count++; } prev = current; } return count; }

• Here’s another way to solve the problem: