How does Java use the contains() function of the String class to determine whether a string contains a specified substring?

The String class in Java provides many commonly used methods to process strings, including the contains() function to determine whether a string contains a specified substring. In this article, we will introduce in detail how to use the contains() function to determine whether a string contains a certain substring, and provide corresponding code examples.

First, let us understand the usage of the contains() function. It is a member function of the String class, used to determine whether a string contains a specified substring. The return value of this function is of Boolean type. If the string contains the specified substring, it returns true; otherwise, it returns false. The specific usage of the contains() function is as follows:

public boolean contains(CharSequence sequence)

Among them, the sequence parameter represents the substring to be checked. It should be noted that the contains() function is case-sensitive, that is, the upper and lower case of characters must match exactly to return true.

Next, let’s take a look at how to use the contains() function to determine whether a string contains a specified substring. We can do this by creating a String object and calling the contains() function. The following is a sample code:

public class StringContainsExample {
    public static void main(String[] args) {
        String str = "Hello, World!";
        String subStr = "Hello";
        
        if (str.contains(subStr)) {
            System.out.println("字符串包含子串");
        } else {
            System.out.println("字符串不包含子串");
        }
    }
}

In the above code, we create a string object named str whose content is "Hello, World!". We also created a string object named subStr with the content "Hello". Then, we use the contains() function to determine whether str contains subStr. If it does, it will output "the string contains the substring"; otherwise, it will output "the string does not contain the substring".

Run the above code, we will get the following output:

字符串包含子串

The above example code is just a simple application of the contains() function. In fact, we can also use the contains() function to perform more operations, such as determining whether a string contains multiple substrings, determining whether a string contains specific characters, etc.

To summarize, the contains() function is an important member function of the String class in Java, used to determine whether a string contains a specified substring. By calling the contains() function, we can easily determine whether the string meets our needs. In actual development, we should be proficient in the usage of the contains() function and apply it flexibly according to specific situations. In the process of processing strings, the contains() function can help us write programs more efficiently and improve our development efficiency.

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