- An array is a
serie of variables of
identical type that are
stored
consecutively in
memory:
- Since char is
a data type in Java,
we can define
an array of char
as follows:
- String:
- Fact:
- The content of
Strings and
arrays of char are
very similar
- Because of their
similarity,
Strings and
arrays of char are
treated
identically
in some programming languages
Example:
- A string and
an array of char are
identical in the
C/C++ programming language
(In C/C++, the programming language defines an pointer arithmetic on pointer variables to make:
char* s; (a string) char s[]; (a character array)become equivalent constructs)
- A string and
an array of char are
identical in the
C/C++ programming language
- The content of
Strings and
arrays of char are
very similar
- However, although a string and an array of char resemble each other, you can decide to treat them differently.
- String and
array of char are
treated
differently in
Java
- Example of differences:
- In Java:
- a
String is a
single object
- an array of char are a serie (multiple) of variables
- a
String is a
single object
- In Java:
- a
String is
immutable
(because the
instance methods
in the String class
will not update the characters
inside a String
- an array of char is not protected by a private access modifier (so we can update the characters stored in an array of char)
- a
String is
immutable
(because the
instance methods
in the String class
will not update the characters
inside a String
- In Java:
- Because Java treats
Strings and
arrays of char
differently,
we need a
conversion mechanism
to tell the Java compiler to
convert one into
another.
(No conversion mechanism is necessary in C/C++ to make strings into arrays of char and vice versa).
- (Instance) method in Java that
converts
a string into an
array of char:
String s; s = "...."; s.toCharArray( ) returns an array of char containing all characters in string sExample:
String s; s = "abc"; char[] A; A = s.toCharArray( ); // Result: A[0] = 'a', A[1] = 'b', A[2] = 'c'
- To "convert" an
array of char
into a String object,
we use a
constructor method
in the String class:
Example:
char[] A = new char[ 3 ]; A[0] = '?'; A[1] = '>'; A[2] = "a"; String s s = new String( A ); // Make a String using the characters in array A
- Example: Java program
public class ArrayChar1 { public static void main( String[] args ) { String s = "abc"; char[] A; /* ========================================= Convert String s into an array of char ========================================= */ A = s.toCharArray(); System.out.println( s ); for ( int i = 0; i < A.length; i++ ) System.out.println( "A[" + i + "] = " + A[i] ); System.out.println( "\n" ); /* ========================================= Convert an array of char A into string ========================================= */ A = new char[4]; A[0] = '>'; A[1] = '<'; A[2] = '?'; A[3] = 'a'; s = new String( A ); for ( int i = 0; i < A.length; i++ ) System.out.println( "A[" + i + "] = " + A[i] ); System.out.println( s ); } }
- Example Program:
(Demo above code)
- Prog file: click here
How to run the program:
- Right click on link and
save in a scratch directory
- To compile: javac ArrayChar1.java
- To run: java ArrayChar1
- It is not advisable
to manipulate strings by
converting it into
an array of char
- That is because:
- the String class
contains
many instance method, and
- there are other classes in the Java library that manipulate Strings.
In other words:
- The chances are very good
that the Java library contains
instance methods
that help you
write your program
It you use an array of char, you will be manipulating the characters in the string and you will need to write the methods (to manipulate the string yourself....
- Nobody likes to write his/her own methods when he/she can use existing ones to do the job !!!
- the String class
contains
many instance method, and