Remove all vowels in a string with Java

问题

I am doing a homework assignment for my Computer Science course. The task is to get a users input, remove all of the vowels, and then print the new statement.

I know I could easily do it with this code:

string.replaceAll("[aeiou](?!\\b)", "")

But my instructor wants me to use nested if and else if statements to achieve the result. Right now I am using something like this:

if(Character.isLetter('a')){
    'do something'
}else if(Character.isLetter('e')){
    'do something else'

But I am not sure what to do inside the if and else if statements. Should I delete the letter? Or is there a better way to do this?

Seeing as this is my homework I don't want full answers just tips. Thanks!

回答1:

Character.isLetter('a')

Character.isLetter(char) tells you if the value you give it is a letter, which isn't helpful in this case (you already know that "a" is a letter).

You probably want to use the equality operator, ==, to see if your character is an "a", like:

char c = ...
if(c == 'a') {
    ...
} else if (c == 'e') {
    ...
}

You can get all of the characters in a String in multiple ways:

As an array with String.toCharArray()
Getting each character from the String using String.charAt(index)

回答2:

I think what he might want is for you to read the string, create a new empty string (call it s), loop over your input and add all the characters that are not vowels to s (this requires an if statement). Then, you would simply print the contents of s.

Edit: You might want to consider using a StringBuilder for this because repetitive string concatenation can hinder performance, but the idea is the same. But to be honest, I doubt it would make a noticeable difference for this type of thing.

回答3:

I think you can iterate through the character check if that is vowel or not as below:

  define a new string 
  for(each character in input string)
    //("aeiou".indexOf(character) <0) id one way to check if character is consonant
    if "aeiou" doesn't contain the character  
      append the character in the new string

回答4:

If you want to do it in O(n) time

Iterate over the character array of your String
If you hit a vowel skip the index and copy over the next non vowel character to the vowel position.
You will need two counters, one which iterates over the full string, the other which keeps track of the last vowel position.
After you reach the end of the array, look at the vowel tracker counter - is it sitting on a vowel, if not then the new String can be build from index 0 to 'vowelCounter-1'.

If you do this is in Java you will need extra space to build the new String etc. If you do it in C you can simply terminate the String with a null character and complete the program without any extra space.

回答5:

I don't think your instructor wanted you to call Character.isLetter('a') because it's always true.

The simplest way of building the result without regexp is using a StringBuilder and a switch statement, like this:

String s = "quick brown fox jumps over the lazy dog";
StringBuffer res = new StringBuffer();
for (char c : s.toCharArray()) {
    switch(c) {
        case 'a': // Fall through
        case 'u': // Fall through
        case 'o': // Fall through
        case 'i': // Fall through
        case 'e': break; // Do nothing
        default: // Do something
    }
}
s = res.toString();
System.out.println(s);

You can also replace this with an equivalent if, like this:

if (c!='a' && c!='u' && c!='o' && c!='i' && c!='e') {
    // Do something
}

来源：https://stackoverflow.com/questions/13167495/remove-all-vowels-in-a-string-with-java

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