Finding Index of last character in an input string JAVA?

问题

I'm trying to figure out how I can find the index of the last character in the first word in a String variable, while using Scanner class to get the String. In my code I need to use a single String for full name, and find the index of the last character in the first name.

So far I made this:

String fullName;
        
Scanner s = new Scanner(System.in);
        
System.out.println("Insert full name: "); //For example: Joseph Adams.

fullName = s.nextLine();
    
int position = fullName.indexOf(" ");

System.out.println(fullName.substring(0, position)); 
//I need to find the index of h in Joseph.

回答1:

Find the index of the last character of the first word

Try this.

the first method subtracts one from the index of the first space which would be the letter h.
the second method splits the string into two parts. Part[0] is joseph. So the h is at the length of that string less 1.

String str = "Joseph Adams";
int index = str.indexOf(" ");
if(index < 0) {
   index = str.length();
}
System.out.println(index-1);

// or

String[] parts = str.split("\\s+");
int len = parts[0].length();
System.out.println(len-1);

Prints

5
5

回答2:

If there is a space in the input name, the index of the character just before space will be position - 1; otherwise (i.e. when fullName.indexOf returns -1), you can print the index of the last character in the input name and/or do some processing (e.g. print some message) as per your requirement.

Demo:

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner s = new Scanner(System.in);
        System.out.print("Insert full name: "); // For example: Joseph Adams.
        String fullName = s.nextLine();
        int position = fullName.indexOf(" ");

        if (position != -1) {
            System.out.println("The index of the character just before space in the input name is " + (position - 1));
        } else {
            System.out.println("There is no space in the input name.");
            System.out.println("The index of the last character in the input name is " + (fullName.length() - 1));
        }
    }
}

A sample run:

Insert full name: Joseph Adams
The index of the character just before space in the input name is 5

Another sample run:

Insert full name: Joseph
There is no space in the input name.
The index of the last character in the input name is 5

回答3:

The index of the last character in the string is just str.length() - 1. For example, to find the index of the h in "Joseph":

public static int indexOfLast(String str){
   return str.length() - 1;                
}

The length of "Joseph" is 6 but there is no character at index 6 (Strings, like arrays, start with the first element at index 0). So, we subtract 1to get 5, which is the final character in the String. So doing:

String name = "Joseph";
name.charAt(indexOfLast(name));

will return h.

来源：https://stackoverflow.com/questions/65351199/finding-index-of-last-character-in-an-input-string-java

标签

java

java.util.scanner

indexof