Java documentation interpretation: Detailed explanation of the length() method of the String class

Java document interpretation: Detailed explanation of the length() method of the String class

The String class is one of the most commonly used classes in the Java language. It provides a series of pairs of characters. Methods to operate on strings. Among them, the length() method is one of the commonly used methods in the String class. This article will provide a detailed explanation of the length() method of the String class and provide specific code examples.

1. Definition of length() method
In the Java documentation, the length() method of the String class is defined as follows:
public int length()

This method returns characters The length of the string, that is, the number of characters in the string. This method does not accept any parameters.

2. Examples of using the length() method
Below we demonstrate the use of the length() method through several specific code examples.

Example 1:
String str = "Hello World";
int len ​​= str.length();
System.out.println("The length of the string is:" len );

Output result:
The length of the string is: 11

In this example, we create a string named "Hello World" and pass length( ) method obtains the length of the string. Finally, we print the length of the string to the console.

Example 2:
String str = "";
int len ​​= str.length();
System.out.println("The length of the string is: " len);

Output result:
The length of the string is: 0

In this example, we create an empty string and obtain the length of the string through the length() method length. Since an empty string contains no characters, the length of the string is 0.

Example 3:
String str = null;
int len ​​= str.length();
System.out.println("The length of the string is: " len);

Output result:
NullPointerException (exception information)

In this example, we assign a null reference to the string variable str. When executing the length() method, because str is null, a NullPointerException will be thrown.

3. Precautions for using the length() method
You need to pay attention to the following points when using the length() method:

1. If the string is null, call length () method will throw NullPointerException. Therefore, make sure the string is not null before calling the length() method.
2. The length() method returns the number of characters in the string, not the number of bytes. If you need to get the byte length of a string, you can use the getBytes() method.
3. The length returned by the length() method is the number of characters in the string, including spaces and special characters. If you want to get the actual number of characters in a string, you can use the getBytes(Charset charset) method to convert the string to the specified character set and get the length of the converted byte array.

Summary:
This article provides a detailed interpretation of the length() method of the String class in the Java document and provides specific code examples. By studying this article, readers can better understand and master the use of length() method. But it should be noted that when using the length() method, be careful to avoid null references and understand the concept of length being the number of characters. Hope this article is helpful to readers!

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