Lecture 9 Part 2: String

Reference

Reading

Characters and Strings(and its links) (only read the part about Strig)

Length of String, characters of strings and substrings

length() returns the length of a String. Notice that length() is a method while array.length is a member of an array.
char charAt(int index) returns the character at the specified index.
String substring(int beginIndex), String substring(int beginIndex, int endIndex) return a new string that is a substring of this string. The substring begins at the specified beginIndex and extends to the character at index endIndex - 1.
char[] toCharArray() converts this string to a new character array.

Example
What is the output of the following program:

public class StringTest1 {
    public static void main(String[] args) {
        String s = "This is a test.";
	System.out.println(s.length());
	System.out.println(s.charAt(3));
	System.out.println(s.substring(3));
	System.out.println(s.substring(3,7));
	char[] charray = s.toCharArray();
	System.out.println(charray[5]);
    }
}

Answer:

15
s
s is a test.
s is
i

Write a program to count the number of 'a' appears in the following paragraph :

The changing of the guard began in earnest Thursday with 
Arnold Schwarzenegger introducing  a team led by a veteran 
political insider that will shepherd the actor's transition to governor 
as soon as this week's recall election is certified.

public class StringTest2 {
    public static void main(String[] args) {
       // break the line in few strings
           String s = "The changing of the guard began in earnest Thursday with " + 
	                   "Arnold Schwarzenegger introducing a team led by a veteran " +
			   "political insider that will shepherd the actor's transition to governor " +
			   "as soon as this week's recall election is certified.";
	int count = 0;
	for(int i = 0; i < s.length(); i++) {
	    if(s.charAt(i) == 'a') {
		count++;
	    }
	}
	System.out.println("There are " + count + "a.");
    }
}

Output

There are 17a.

Searching

indexOf(int ch),indexOf(int ch, int fromIndex),lastIndexOf(int ch), lastIndexOf(int ch, int fromIndex), indexOf(String str), indexOf(String str, int fromIndex),indexOf(String str, int fromIndex),lastIndexOf(String str, int fromIndex): return the index of the first occurrence (or last occurrence) of the character( or string) or -1 if the character (string) doesn't occur.

What is the output of the following program?

public class StringTest3 {
    public static void main(String[] args) {
	String s = "C++ is a good computer language. Java is the best computer language!"; 
	
	System.out.println(s.indexOf('a'));
	System.out.println(s.indexOf('a', 20));
	System.out.println(s.lastIndexOf('u'));
	System.out.println(s.lastIndexOf('o', 20));
	System.out.println(s.indexOf("computer"));
	System.out.println(s.lastIndexOf("computer"));
	System.out.println(s.lastIndexOf("abcdefg"));
    }
}

Answer

For the following list of names, write a program to print out the last names:

String[] names = {"George Washington", "Abraham Lincoln", "Bill Clinton", "Ronald Reagan","Thomas Jefferson", "George Bush"};

Answer

public class LastName {
    public static void main(String[] args) {
        String[] names = {"George Washington", "Abraham Lincoln", "Bill Clinton",
                               "Ronald Reagan","Thomas Jefferson", "George Bush"};
        for(int i =0; i < names.length; i++) {
	    System.out.println(names[i].substring(names[i].lastIndexOf(" ")+1));
	}
    }
}

Output

Washington
Lincoln
Clinton
Reagan
Jefferson
Bush

Test

equals(String anotherString), equalsIgnoreCase(String anotherString)
int compareTo(String anotherString), int compareToIgnoreCase(String str): The result is a negative integer if this String object lexicographically precedes the argument string. The result is a positive integer if this String object lexicographically follows the argument string. The result is zero if the strings are equal;
startsWith(String prefix), startsWith(String prefix, int toffset),endsWith(String suffix)

Creating new String

String toUpperCase(), String toLowerCase()
String concat(String str):Concatenates the specified string to the end of this string. Similar to +.
String replace(char oldChar, char newChar) returns a new string resulting from replacing all occurrences of oldChar in this string with newChar.
String trim() returns a copy of the string, with leading and trailing whitespace omitted.

What is the output of the following program?

public class StringTest4 {
    public static void main(String[] args) {
	String s = "PIC10A is cool!";
	System.out.println(s);
	System.out.println(s.toLowerCase());
	System.out.println(s.toUpperCase());
	System.out.println(s.replace('o','a'));
	System.out.println(s);
    }
}

Output

PIC10A is cool!
pic10a is cool!
PIC10A IS COOL!
PIC10A is caal!
PIC10A is cool!

Remark You can't change the content of a String. You can only assign a new reference to it.