View RSS Feed

penguinCoder

String Cheat Sheet

Rate this Entry
by , 10-18-2012 at 12:05 AM (1871 Views)
A string is a piece of text, that is zero or more characters in length. In Java, strings are considered to be pre-built objects. The variable for a string does not store the value of the string, rather it is a reference point, or pointer, to the storage location of where the string is kept.


Declaring a String:
Java Code:
String s1;
Assigning a Value On Declaration:
Java Code:
String s1 = "Hello World!";
Assigning a Value With Assignment
Java Code:
String s1;
s1 = "Hello World!";
Assigning a Value With Input
[code]
String s1;
s1 = keyboard.next();
[code]


Common String Methods

The string class is 'immutable', which means that none of the different methods that strings use can change what is actually stored within the string itself. When methods alter a string, rather then saving it in the same storage location, it chooses a new storage location, and leaves the original unchanged. Any method that seems to change a string's contents is actually producing a modified version in an independent storage.


To identify how many characters reside in a particular strings, use the following method.
Java Code:
int len;
String s1;
len = s1.length();
This will store the number of characters that are stored in the string s1 and store that number in the integer len.
Individual Character


You are able to extract single characters from within a string, and you can even choose which character to extract; based upon the index number of the string.
Java Code:
char extr;
String s1;
int ix;
extr = s1.charAt(ix);
This extracts the character with the index number ix, remember that the index number starts at 0 for the first character. The character would be saved in the variable extr.


Comparing Contents
You can compare strings in couple of different ways.

The way that you will most often use is to compare the contents of the string. You are able to do that using the following method.
Java Code:
String s1, s2;
if( s1.equals( s2 ) )
    System.out.println("Same string contents");
The other way is to compare the addresses that are stored in the variable itself. This is a lot less common, and mainly used in the mistaken idea that it will compare the contents of the string. To compare storage locations of strings use the following method.
Java Code:
String s1, s2;
if( s1 == s2 )
    System.out.println("Same Addresses");
Another way that you can compare strings is by their alphabetic order. This type or comparison sorts the strings from A-Z. This is done utilizing the following method.
Java Code:
String s1, s2;
int compare;
compare = s1.compareTo( s2 );
if( compare < 0 )
    System.out.println("s1 is less than s2");
else if( compare > 0 )
    System.out.println("s2 is less than s1");
else //compares for s1 == s2
    System.out.println("s1 is the same as s2");

Converting Case

Another thing that you are able to do with strings is to convert their case. You can covert all the characters to uppercase, or convert all the characters to lowercase. This is done using the following method.
Java Code:
String s1, s2, s3;
s2 = s1.toUpperCase();
s3 = s1.toLowerCase();
This does not change the string that is stored at the memory location s1; rather it makes two new strings and creates two new storage locations. An independent copy that is all lowercase is stored at memory location s3, while an independent copy that is all uppercase is stored at memory location s2.


Changing a String

You can add to a String using the '+=' format.
Java Code:
String s1 = "Hello";
s1 += " World";
You can also replace the entire String using the '=' format.
Java Code:
String s1 = "Hello";
s1 = "Hello World";

Submit "String Cheat Sheet" to Facebook Submit "String Cheat Sheet" to Digg Submit "String Cheat Sheet" to del.icio.us Submit "String Cheat Sheet" to StumbleUpon Submit "String Cheat Sheet" to Google

Updated 10-18-2012 at 12:29 AM by penguinCoder

Categories
Cheat Sheet

Comments