Common operation methods for sorting out strings in Java programming

character
Generally, when we process characters, we use the original data type char.

Example

 char ch = 'a';// Unicode for uppercase Greek omega characterchar uniChar = '/u039A'; // an array of charschar[] charArray ={ 'a', 'b', 'c', 'd', 'e' };

However, in development, we will encounter situations where we need to use objects instead of primitive data types. To meet this need. Java provides a wrapper class Character for the original data type char.

The Character class provides a series of useful classes (for example: static classes). You can create a Character object with the help of the Character constructor.

 Character ch = new Character('a');

The Java compiler will also be able to create a Character object for you in some cases. For example: If you transfer a raw char to a method that can be expected, the compiler will automatically convert the char to a Character for you. If the conversion takes place in the opposite direction, this feature is called automatic packing or unboxing.

Example

 // Here following primitive char 'a'// is boxed into the Character object chCharacter ch = 'a';// Here primitive 'x' is boxed for method test,// return is unboxed to char 'c'char c = test('x');

Escape sequence
The character with a backslash (/) before is an escape sequence and has special meaning for the compiler.

Line breaks (/n) are often used in the System.out.println() statement, and line breaks after strings are printed.

The following table shows the Java escape sequence:

Example

If you want to put quotes inside, you must use escape sequences, /" , quote internally:

 public class Test { public static void main(String args[]) { System.out.println("She said /"Hello!/" to me."); }}

This will produce the following results:

She said "Hello!" to me.
Character Methods The following list is an important example method that implements all subclasses of the Character class:

String
String, which is widely used in Java programming, is a sequence of characters. In the Java programming language, strings are objects.

The Java platform provides String classes to create and manipulate strings.

Create a string
The most direct way to create a string is written like this:

String greeting = "Hello world!";
When you create a string, the compiler creates a String object with its value in this case, such as: "Hello world!'.

Any other object can be created by using the new keyword and by constructor. The String class has 11 constructors that provide initial values ​​using different types of strings, such as an array of characters.

 public class StringDemo{ public static void main(String args[]){ char[] helloArray = { 'h', 'e', ​​'l', 'l', 'o', '.'}; String helloString = new String(helloArray); System.out.println( helloString ); }}

This will produce the following results:

 hello.

Note The String class is immutable, so once a String object is created, it cannot be changed. If you need to modify a string with a large number of characters, you should use the StringBuffer & StringBuilder class.

String length
The method used to obtain information about an object is called an access method. One access method that can be used with a string is length() , which returns the number of characters contained in a string object.

After the following two lines of code are executed, len equals 17:

 public class StringDemo { public static void main(String args[]) { String palindrome = "Dot saw I was Tod"; int len ​​= palindrome.length(); System.out.println( "String Length is : " + len ); }}

This will produce the following results:

 String Length is : 17

Connection string
The String class includes methods for concatenating two strings:

 string1.concat(string2);

This returns a new string, which adds string2 at the end of string1. You can also use the concat() method to concatenate strings, such as:

 "My name is ".concat("Zara");

Strings are more often concatenated with the "+" operator, such as:

 "Hello," + " world" + "!"

This will produce:

 "Hello, world!"

Take a look at the following example:

 public class StringDemo { public static void main(String args[]) { String string1 = "saw I was "; System.out.println("Dot " + string1 + "Tod"); }}

This will produce the following results:

 Dot saw I was Tod

Create a formatted string
There are already printf() and format() methods to print out the output format numbers. The String class has an equivalent method format(), which returns a String object instead of a PrintStream object.

The static format() method using strings allows the creation of reusable formatted strings instead of a one-time print statement. For example, if instead of the following method:

 System.out.printf("The value of the float variable is " + "%f, while the value of the integer " + "variable is %d, and the string " + "is %s", floatVar, intVar, stringVar);

You can write this way:

 String fs;fs = String.format("The value of the float variable is " + "%f, while the value of the integer " + "variable is %d, and the string " + "is %s", floatVar, intVar, stringVar);System.out.println(fs);

String method
Here is a list of methods supported by the String class: