Getting to know Java for the first time (Java String - Get String Information)

First, get string information

    Strings are used as objects, and the effective information of the string can be obtained through corresponding methods, such as obtaining the length of a string, the characters at a certain index position, and so on.

    1.1 Get the length of the string

    Use the length() method of the String class to obtain the length of a declared string object.

    Syntax: str.length();

    str : String object

String str = "We are Happy!";
int size = str.length(); //Assign the length of the string str to the int variable size

      The value of size is equal to 13, which means that the length of the string returned by the length() method includes spaces in the string.

    1.2 String lookup

    The String class provides two methods for finding strings, the indexOf() and lastIndexOf() methods. Both of these methods allow searching within a string for a character or string of specified criteria. The indexOf() method returns the position of the first occurrence of the searched character or string, and the lastindexOf() method returns the position of the last occurrence of the searched character or string.

    1.2.1 indexOf ( String s )

    This method is used to return the index position of the first occurrence of the parameter string s in the specified string. When the indexOf() method of a string is called, the position of s is searched from the beginning of the current string; if the string s is not retrieved, the return value of this method is -1.

    Syntax: str.indexOf(substr)    

    str : any string object

    substr : the string to search for

    1.2.2 lastindexOf( String str)

    This method returns your index position of the last early summer of the specified string. When the string's lastindexOf() method is called, the parameter character str is retrieved from the beginning of the current string, and the index of the last occurrence of str is returned. If the string str is not retrieved, the method returns -1.

    Syntax: str.lastindexOf( substr )

    str : an arbitrary string object

    substr : the string to search for

public class Text{ //Create class
    public static void main(String [] args){ //Main method
        String str = "We are students"; //Define the string str
        int size1 = str.indexOf("a"); //Assign the index position of a in the string str to the variable size1  
        int size2 = str.lastindexOf(""); //Assign the index position of the empty string in str to the variable size2
        System.out.println("The index position of a character in the string str is: "+size1); //Output the variable size1
        System.out.println("The index position of the empty string in the string str is: "+size2); //Output the variable size2
        System.out.println("The length in the string str is: "+str.length()); //Output the length of str
    }
}

    The running result is:

The character's index position in the string str is: 3
The index position of the null character in the string str is: 15
The length of the string str is: 15

    If the parameter in the lastindexOf() method is the empty string "" (note no spaces), the result returned is the same as the result of calling the length() method on that string.

    1.3 Get the character at the specified index position

    Use the charAt() method to return the character at the specified index.

    Syntax: str.charAt(int index) 

    str : any string

    index : an integer value that specifies the subscript of the character to be returned

public class Ref{ //Create class
    public static void main(String[] args){ //Main method
        String str = "hello word"; //Define the string str
        char mychar = str.charAt(5); //return the character at index position 5 in the string str
        System.out.println("The character at index position 5 in the string str is: "+mychar); //Output information
    }
}

    The result of the operation is:  the character at index position 5 in the string str is: w

    For learning Java, read books, watch videos, watch official documents, watch API, practice more, think more.

    Always learn, update quickly, learn new technologies, work hard, and I wish you will become a great god in the end.