使用Java提取数字或单词的逗号分隔列表

Question

for example with the given input message: hello java 2017 ** 2020 world

• When choice == 2 output 2017 , 2020
• when choice == 3 output hello , java , world

Here is my program:

public static void print(String message, int choice){
    {    
        for (int i = 0; i < message.length();) {
            if (message.indexOf(" ") != -1) {
                System.out.print(message.substring(0, message.indexOf(" ")));
                message = message.substring(message.indexOf(" ") + 1);
                switch (choice) {
                    case 2: {
                        char c;
                        for (int k = 0; k < message.length(); k++) {
                            c = message.charAt(k);
                            if (Character.isDigit(c)) {
                                System.out.print(c+" , ");
                            }break;
                        }
                    }
                    case 3: {    
                        for (int z = 0; z < message.length(); z++) {
                            char tr = message.charAt(z);
                            if (Character.isAlphabetic(tr)) {

                                System.out.print(tr);
                                break;
                            }
                        }
                    }
                }
            } else {
                System.out.println(message);
                break;
            }
        }
    }
}

I want to do it without using split , replace , arrays or a tokenizer .

Answer 1

Regex?

You can match numbers with (\\\\d+) in Java and words (assuming from your example that it will contain only alphabetical characters with ([a-zA-z]+)

Now you can go ahead and do the following:

public static void print(String message, int choice) {
    switch (choice) {
        case 2:
            Pattern p = Pattern.compile("(\\d+)");
            Matcher m = p.matcher(message);
            while (m.find()) {
                System.out.println(m.group());
            }
            break;
        case 3:
            Pattern p2 = Pattern.compile("([a-zA-z]+)");
            Matcher m2 = p2.matcher(message);
            while (m2.find()) {
                System.out.println(m2.group());
            }
            break;
    }
}

Instead of printing the groups, you can as well add them to a list for later use, etc.

However I suggest (as others did in the comments before) that you use the probably easier and faster tools Java already offers to you.

Testing the above code with your example like this

public static void main(String[] args) {
    String s = "hello java 2017 ** 2020 world";
    print(s, 2);
    System.out.println();
    print(s, 3);
}

prints:

2017
2020

hello
java
world

Again you can put those in a List or other type of collection for later use including the comma separation.