Strings, which are widely used in Java programming, are a sequence of characters. In the Java programming language, strings are objects.
The Java platform provides the
char[] helloArray = { 'h', 'e', 'l', 'l', 'o', '.' }; String helloString = new String[helloArray]; System.out.println[helloString];1 class to create and manipulate strings.
Creating Strings
The most direct way to create a string is to write:
String greeting = "Hello world!";
In this case, "Hello world!" is a string literal—a series of characters in your code that is enclosed in double quotes. Whenever it encounters a string literal in your code, the compiler creates a
char[] helloArray = { 'h', 'e', 'l', 'l', 'o', '.' }; String helloString = new String[helloArray]; System.out.println[helloString];1 object with its value—in this case,
char[] helloArray = { 'h', 'e', 'l', 'l', 'o', '.' }; String helloString = new String[helloArray]; System.out.println[helloString];3.
As with any other object, you can create
char[] helloArray = { 'h', 'e', 'l', 'l', 'o', '.' }; String helloString = new String[helloArray]; System.out.println[helloString];1 objects by using the
char[] helloArray = { 'h', 'e', 'l', 'l', 'o', '.' }; String helloString = new String[helloArray]; System.out.println[helloString];5 keyword and a constructor. The
char[] helloArray = { 'h', 'e', 'l', 'l', 'o', '.' }; String helloString = new String[helloArray]; System.out.println[helloString];1 class has thirteen constructors that allow you to provide the initial value of the string using different sources, such as an array of characters:
char[] helloArray = { 'h', 'e', 'l', 'l', 'o', '.' }; String helloString = new String[helloArray]; System.out.println[helloString];
The last line of this code snippet displays
char[] helloArray = { 'h', 'e', 'l', 'l', 'o', '.' }; String helloString = new String[helloArray]; System.out.println[helloString];7.
char[] helloArray = { 'h', 'e', 'l', 'l', 'o', '.' }; String helloString = new String[helloArray]; System.out.println[helloString];1 class is immutable, so that once it is created a
char[] helloArray = { 'h', 'e', 'l', 'l', 'o', '.' }; String helloString = new String[helloArray]; System.out.println[helloString];1 object cannot be changed. The
char[] helloArray = { 'h', 'e', 'l', 'l', 'o', '.' }; String helloString = new String[helloArray]; System.out.println[helloString];1 class has a number of methods, some of which will be discussed below, that appear to modify strings. Since strings are immutable, what these methods really do is create and return a new string that contains the result of the operation.
String Length
Methods used to obtain information about an object are known as accessor methods. One accessor method that you can use with strings is the
String palindrome = "Dot saw I was Tod"; int len = palindrome.length[];1 method, which returns the number of characters contained in the string object. After the following two lines of code have been executed,
String palindrome = "Dot saw I was Tod"; int len = palindrome.length[];2 equals 17:
String palindrome = "Dot saw I was Tod"; int len = palindrome.length[];
A palindrome is a word or sentence that is symmetric—it is spelled the same forward and backward, ignoring case and punctuation. Here is a short and inefficient program to reverse a palindrome string. It invokes the
char[] helloArray = { 'h', 'e', 'l', 'l', 'o', '.' }; String helloString = new String[helloArray]; System.out.println[helloString];1 method
String palindrome = "Dot saw I was Tod"; int len = palindrome.length[];4, which returns the ith character in the string, counting from 0.
public class StringDemo { public static void main[String[] args] { String palindrome = "Dot saw I was Tod"; int len = palindrome.length[]; char[] tempCharArray = new char[len]; char[] charArray = new char[len]; // put original string in an // array of chars for [int i = 0; i < len; i++] { tempCharArray[i] = palindrome.charAt[i]; } // reverse array of chars for [int j = 0; j < len; j++] { charArray[j] = tempCharArray[len - 1 - j]; } String reversePalindrome = new String[charArray]; System.out.println[reversePalindrome]; } }
Running the program produces this output:
To accomplish the string reversal, the program had to convert the string to an array of characters [first
String palindrome = "Dot saw I was Tod"; int len = palindrome.length[];5 loop], reverse the array into a second array [second
String palindrome = "Dot saw I was Tod"; int len = palindrome.length[];5 loop], and then convert back to a string. The
char[] helloArray = { 'h', 'e', 'l', 'l', 'o', '.' }; String helloString = new String[helloArray]; System.out.println[helloString];1 class includes a method,
String palindrome = "Dot saw I was Tod"; int len = palindrome.length[];8, to convert a string, or a portion of a string, into an array of characters so we could replace the first
String palindrome = "Dot saw I was Tod"; int len = palindrome.length[];5 loop in the program above with
palindrome.getChars[0, len, tempCharArray, 0];
Concatenating Strings
The
char[] helloArray = { 'h', 'e', 'l', 'l', 'o', '.' }; String helloString = new String[helloArray]; System.out.println[helloString];1 class includes a method for concatenating two strings:
This returns a new string that is string1 with string2 added to it at the end.
You can also use the
public class StringDemo { public static void main[String[] args] { String palindrome = "Dot saw I was Tod"; int len = palindrome.length[]; char[] tempCharArray = new char[len]; char[] charArray = new char[len]; // put original string in an // array of chars for [int i = 0; i < len; i++] { tempCharArray[i] = palindrome.charAt[i]; } // reverse array of chars for [int j = 0; j < len; j++] { charArray[j] = tempCharArray[len - 1 - j]; } String reversePalindrome = new String[charArray]; System.out.println[reversePalindrome]; } }1 method with string literals, as in:
"My name is ".concat["Rumplestiltskin"];
Strings are more commonly concatenated with the
public class StringDemo { public static void main[String[] args] { String palindrome = "Dot saw I was Tod"; int len = palindrome.length[]; char[] tempCharArray = new char[len]; char[] charArray = new char[len]; // put original string in an // array of chars for [int i = 0; i < len; i++] { tempCharArray[i] = palindrome.charAt[i]; } // reverse array of chars for [int j = 0; j < len; j++] { charArray[j] = tempCharArray[len - 1 - j]; } String reversePalindrome = new String[charArray]; System.out.println[reversePalindrome]; } }2 operator, as in
"Hello," + " world" + "!"
which results in
The
public class StringDemo { public static void main[String[] args] { String palindrome = "Dot saw I was Tod"; int len = palindrome.length[]; char[] tempCharArray = new char[len]; char[] charArray = new char[len]; // put original string in an // array of chars for [int i = 0; i < len; i++] { tempCharArray[i] = palindrome.charAt[i]; } // reverse array of chars for [int j = 0; j < len; j++] { charArray[j] = tempCharArray[len - 1 - j]; } String reversePalindrome = new String[charArray]; System.out.println[reversePalindrome]; } }2 operator is widely used in
public class StringDemo { public static void main[String[] args] { String palindrome = "Dot saw I was Tod"; int len = palindrome.length[]; char[] tempCharArray = new char[len]; char[] charArray = new char[len]; // put original string in an // array of chars for [int i = 0; i < len; i++] { tempCharArray[i] = palindrome.charAt[i]; } // reverse array of chars for [int j = 0; j < len; j++] { charArray[j] = tempCharArray[len - 1 - j]; } String reversePalindrome = new String[charArray]; System.out.println[reversePalindrome]; } }4 statements. For example:
String string1 = "saw I was "; System.out.println["Dot " + string1 + "Tod"];
which prints
Such a concatenation can be a mixture of any objects. For each object that is not a
char[] helloArray = { 'h', 'e', 'l', 'l', 'o', '.' }; String helloString = new String[helloArray]; System.out.println[helloString];1, its
public class StringDemo { public static void main[String[] args] { String palindrome = "Dot saw I was Tod"; int len = palindrome.length[]; char[] tempCharArray = new char[len]; char[] charArray = new char[len]; // put original string in an // array of chars for [int i = 0; i < len; i++] { tempCharArray[i] = palindrome.charAt[i]; } // reverse array of chars for [int j = 0; j < len; j++] { charArray[j] = tempCharArray[len - 1 - j]; } String reversePalindrome = new String[charArray]; System.out.println[reversePalindrome]; } }6 method is called to convert it to a
char[] helloArray = { 'h', 'e', 'l', 'l', 'o', '.' }; String helloString = new String[helloArray]; System.out.println[helloString];1.
Note: The Java programming language does not permit literal strings to span lines in source files, so you must use the
public class StringDemo { public static void main[String[] args] { String palindrome = "Dot saw I was Tod"; int len = palindrome.length[]; char[] tempCharArray = new char[len]; char[] charArray = new char[len]; // put original string in an // array of chars for [int i = 0; i < len; i++] { tempCharArray[i] = palindrome.charAt[i]; } // reverse array of chars for [int j = 0; j < len; j++] { charArray[j] = tempCharArray[len - 1 - j]; } String reversePalindrome = new String[charArray]; System.out.println[reversePalindrome]; } }2 concatenation operator at the end of each line in a multi-line string. For example:
String quote = "Now is the time for all good " + "men to come to the aid of their country.";
Breaking strings between lines using the
public class StringDemo { public static void main[String[] args] { String palindrome = "Dot saw I was Tod"; int len = palindrome.length[]; char[] tempCharArray = new char[len]; char[] charArray = new char[len]; // put original string in an // array of chars for [int i = 0; i < len; i++] { tempCharArray[i] = palindrome.charAt[i]; } // reverse array of chars for [int j = 0; j < len; j++] { charArray[j] = tempCharArray[len - 1 - j]; } String reversePalindrome = new String[charArray]; System.out.println[reversePalindrome]; } }2 concatenation operator is, once again, very common in
public class StringDemo { public static void main[String[] args] { String palindrome = "Dot saw I was Tod"; int len = palindrome.length[]; char[] tempCharArray = new char[len]; char[] charArray = new char[len]; // put original string in an // array of chars for [int i = 0; i < len; i++] { tempCharArray[i] = palindrome.charAt[i]; } // reverse array of chars for [int j = 0; j < len; j++] { charArray[j] = tempCharArray[len - 1 - j]; } String reversePalindrome = new String[charArray]; System.out.println[reversePalindrome]; } }4 statements.
Creating Format Strings
You have seen the use of the
palindrome.getChars[0, len, tempCharArray, 0];1 and
palindrome.getChars[0, len, tempCharArray, 0];2 methods to print output with formatted numbers. The
char[] helloArray = { 'h', 'e', 'l', 'l', 'o', '.' }; String helloString = new String[helloArray]; System.out.println[helloString];1 class has an equivalent class method,
palindrome.getChars[0, len, tempCharArray, 0];2, that returns a
char[] helloArray = { 'h', 'e', 'l', 'l', 'o', '.' }; String helloString = new String[helloArray]; System.out.println[helloString];1 object rather than a
palindrome.getChars[0, len, tempCharArray, 0];6 object.
Using
palindrome.getChars[0, len, tempCharArray, 0];7 static
palindrome.getChars[0, len, tempCharArray, 0];2 method allows you to create a formatted string that you can reuse, as opposed to a one-time print statement. For example, instead of