How to use the startsWith() method of the String class to determine whether a string starts with a specified prefix

How to use the startsWith() method of the String class to determine whether a string starts with a specified prefix

The String class is a commonly used class in Java. It provides many convenient methods for operating strings. Among them, the startsWith() method is used to determine whether a string starts with the specified prefix. Use this method to easily perform string prefix matching.

The usage of the startsWith() method is very simple. It only requires one parameter, which is the prefix string to be checked. It returns a Boolean value, true if the original string begins with the specified prefix, false otherwise.

The following is a sample code that uses the startsWith() method to determine whether a string begins with a specified prefix:

public class StringStartsWithExample {
    public static void main(String[] args) {
        String str = "Hello, World!";

        // 判断字符串是否以指定的前缀开头
        boolean result = str.startsWith("Hello");

        // 打印结果
        System.out.println("字符串是否以指定的前缀开头: " + result);
    }
}

Run the above code, the following results will be output:

字符串是否以指定的前缀开头: true

In the above example, we define a string str, and then use the startsWith() method to determine whether it starts with "Hello" as the prefix. Since the prefix of str is indeed "Hello", the result returned by the startsWith() method is true.

In addition to determining whether a string begins with the specified prefix, the startsWith() method can also limit the starting position. It provides an overloaded method, namely startsWith(String prefix, int offset). This method takes two parameters, the first parameter is the prefix string to be checked, and the second parameter is the index of the starting position. For example, we can use a substring in the string as the string to be judged by passing the starting position:

public class StringStartsWithExample {
    public static void main(String[] args) {
        String str = "Hello, World!";

        // 从索引位置6开始，判断字符串是否以指定的前缀开头
        boolean result = str.startsWith("World", 6);

        // 打印结果
        System.out.println("字符串是否以指定的前缀开头: " + result);
    }
}

Running the above code will output the following results:

字符串是否以指定的前缀开头: true

In the above In the example, we set the starting position to 6, and then use the startsWith() method to determine whether the substring of the string str starting from position 6 starts with "World" as the prefix. Since the substring does start with "World", the startsWith() method returns true.

In summary, using the startsWith() method of the String class can easily determine whether a string starts with the specified prefix. Its usage is very simple and requires only one parameter. It should be noted that the startsWith() method is case-sensitive, so the prefix string to be determined needs to be exactly the same as the prefix of the original string to return the correct result. In addition, it also provides overloaded methods that can limit the starting position. In practical applications, we can use this method to easily perform string prefix matching operations.

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