Java String class

Strings are widely used in Java programming. Strings are objects in Java. Java provides the String class to create and operate strings.

Create a string

The simplest way to create a string is as follows:

String greeting = "Hello world!";

When you encounter a string constant in the code, the value here is "Hello world!", the compiler will use this value to create a String object.

Like other objects, you can use keywords and construction methods to create String objects.

The String class has 11 construction methods. These methods provide different parameters to initialize the string, such as providing a character array parameter:

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 );
   }
}

The compilation and running results of the above example are as follows:

hello.

Note:The String class is immutable, so once you create a String object, its value cannot be changed. If you need to make a lot of modifications to the string, then you should choose to use the StringBuffer & StringBuilder classes.

String length

The methods used to obtain information about an object are called accessor methods.

An accessor method of the String class is the length() method, which returns the number of characters contained in the string object.

After the following code is executed, the len variable is equal to 14:

public class StringDemo {
    public static void main(String args[]) {
        String site = "www.php.cn";
        int len = site.length();
        System.out.println( "php中文网网址长度 : " + len );
   }
}

The compilation and running results of the above example are as follows:

php中文网网址长度 : 14

Connection string

The String class provides a method for concatenating two strings:

string1.concat(string2);

Returns a new string obtained by connecting string2 to string1. You can also use the concat() method for string constants, such as:

"My name is ".concat("php");

More commonly used is to use the '+' operator to concatenate strings, such as:

"Hello," + " world" + "!"

The result is as follows:

"Hello, world!"

The following is an example:

public class StringDemo {
    public static void main(String args[]) {     
        String string1 = "php中文网网址：";     
        System.out.println("1、" + string1 + "www.php.cn");  
    }
}

The compilation and running results of the above example are as follows:

1、php中文网网址：www.php.cn

Create a formatted string

We know the output formatting Numbers can use the printf() and format() methods. The String class uses the static method format() to return a String object instead of a PrintStream object.

The static method format() of the String class can be used to create reusable formatted strings, not just for one-time print output. As shown below:

System.out.printf("浮点型变量的的值为 " +
                  "%f, 整型变量的值为 " +
                  " %d, 字符串变量的值为 " +
                  "is %s", floatVar, intVar, stringVar);

You can also write like this

String fs;
fs = String.format("浮点型变量的的值为 " +
                   "%f, 整型变量的值为 " +
                   " %d, 字符串变量的值为 " +
                   " %s", floatVar, intVar, stringVar);
System.out.println(fs);

String method

The following are the methods supported by the String class. For more details, see Java String API document: