子串不等于第一个字符的串

Question

I am struggling to figure out what's wrong with my code. When the user input is "apple" I get that it doesn't begin with a vowel.

import java.util.*;
public class StringeExerciseElearn {
    public static void main(String[] args) {
        Scanner k = new Scanner(System.in);
        System.out.println("Type a word: ");
        String input = k.next();
        String l = input.substring(0);
        String a = "a";
        String e = "e";
        String i = "i";
        String o = "o";
        String u = "u";

        if(l.equals(a) || l.equals(e) || l.equals(i) || l.equals(o) || l.equals(u))
            System.out.println(input + " begins with a vowel!");
        else
            System.out.println(input + " doesn't begin with a vowel");
        }
    }
}

Answer 1

Use startWith method of String , it will work fine.

public class Practice {

public static void main(String[] args) {
    // TODO Auto-generated method stub

    Scanner k = new Scanner(System.in);
    System.out.println("Type a word: ");
    String input = k.next();
    String l = input;
    String a = "a";
    String e = "e";
    String i = "i";
    String o = "o";
    String u = "u";

    if (l.startsWith(a) || l.startsWith(e) || l.startsWith(i) || l.startsWith(o) || l.startsWith(u))
        System.out.println(input + " begins with a vowel!");
    else
        System.out.println(input + " doesn't begin with a vowel");
}

Answer 2

input.substring(0) returns the String starting at the index 0 and extending the length of the string. In other words, it returns the input string; eg "apple".substring(0) returns "apple".

To get a single characters substring, you need to use the version of the substring method that takes both a begin index and an end index — public String substring​(int beginIndex, int endIndex) :

String l = input.substring(0, 1);

Note that this will throw an IndexOutOfBoundsException for the empty string ( "" ). To prevent this, the string's length should also be checked before doing the substring check.

Answer 3

You made a mistake using the substring method, you should say the start position in first parameter and the length desires of the substring in second parameter :

String l = input.substring(0, 1);

And now it works fine :) :

Type a word: 
apple
apple begins with a vowel!