The ArrayList Class and the enum Keyword - Learning Java Through Games - page 141

StringBuffer s = new StringBuffer( "hello" );
removeFirstCharacter(s) ;
System. out . println ( s ) ;
}
}
In the example, the removeFirstCharacter method removes the first character of the
string. Note that if the method took as input a String instead of a StringBuffer ,thenit
would be impossible for the method to modify the string and the changes to be seen inside
the main method. The setCharAt method changes the character at the position that is
specified as the first parameter. The setCharAt method is part of the StringBuffer class,
but not the String class. The reason is that the String class is immutable and therefore
cannot be modified. The charAt method is part of both classes and returns the element at
the specified position.
It is worth examining the method removeFirstChracter in detail. When i=1 ,the
method reads the character at position 1 and places it at position 0. Then it reads the
character at position 2 and places at position 1 and so on. In other words, all the characters
except for the first character are shifted to the left by one position. Note that if we first
shifted the last character one to the left, then the whole string will contain just the last
character. Therefore, it is important that we started shifting characters from left to right
and not from right to left. The deleteCharAt method is used to delete the last character.
If the method was not executed, then we would have two copies of the last character at
the last two positions of the string (i.e., gotten the string "elloo" instead of the string
"ello" ). The smart reader has probably noticed that the method removeFirstCharacter
can be significantly shortened.
public static void removeFirstCharacter(StringBuffer s) {
s . delteChraAt(0) ;
}
However, we chose the longer version in order to demonstrate how an element of a list
can be deleted by moving elements.
Note that we cannot use the following syntax for the StringBuffer s.
s= "dog" ;
To put it differently, the String class behaves similar to a primitive type. It can be directly
assigned a value and we do not need to use the new keyword to crate a new string. However,
this is not the case for the StringBuffer class. A new StringBuffer can be created by
passing a string to its constructor.
StringBuffer s = new StringBuffer( "dog" );
As we saw, once a StringBuffer is created, we cannot simply change its value. However,
we can use the append method to append more characters to the StringBuffer .Consider
the following code.
s . append( "cat" );
It will append the string cat to the StringBuffer s . In other words, the StringBuffer s
will now be equal to dogcat .