Difference between StringBuffer (String str) and StringBuffer (CharSequence chars)
A CharSequence
is an interface; it happens that it String
implements it.
This means that, for example, when you call .charAt()
in String
, what is actually called the implementation String
for that method CharSequence
.
As you can see from the javadoc CharSequence
, not many classes in the JDK actually implement this interface.
As for the two constructors, this StringBuffer
is Java 1.0 and CharSequence
only appears in 1.4; however this also applies to StringBuilder
(which you should use instead of StringBuffer
) has two constructors (one with a CharSequence
as an argument, the other with String
c as an argument), so there is probably an optimization when a String
is passed as an argument. For such optimizations, this is the Use Source, Luke (tm) case.
As an example of an implementation CharSequence
that is missing from the JDK, you can, for example, see one of my projects: largetext . Note that, among other things, generating a Matcher
from Pattern
uses CharSequence
rather than String
as an argument ; and since it String
implements CharSequence
, well, passing String
as an argument.
source to share
CharSequence
is an interface, so you cannot create it directly. String
is a concrete class that implements the interface CharSequence
. StringBuffer
also implements the interface CharSequence
.
As for why it StringBuffer
has two constructors, one that takes String
and one that takes CharSequence
, it's almost certainly because (per line Since
in the Javadoc) was CharSequence
n't added until Java v1.4 until StringBuffer
(and String
) were in Java 1.0
source to share
public StringBuffer (String str): Creates a string buffer initialized with the contents of the specified string. The initial capacity of the string buffer is 16 plus the length of the string argument.
public StringBuffer (CharSequence seq): Creates a string buffer containing the same characters as the specified CharSequence. The initial capacity of the string buffer is 16 plus the length of the CharSequence argument. If the length of the specified CharSequence is less than or equal to zero, an empty buffer with a throughput of 16 is returned.
source to share