如何忽略字符串/流中的某些字符？

Question

Let's say, I write some code to print out "Hello World."

Could I use some sort of ignore list of characters to be ignored from my print string (in this case Hello World). For instance, I want to remove the r in "hello wo r ld" so that the output is "Hello Wold"

I have a value that I am using. I have the following characters: &, \\, and *.

I think one of these characters is causing me to have some of my values ignored.

Normally I would just test this myself, but I am not able to do this at this time.

Answer 1

No idea why you would want to do this, but writing a method to do that isn't all that hard...

public static void printlnWithIgnores(String toPrint, Set<Character> ignore) {
    for(char c : toPrint.toCharArray()) {
        if(! ignore.contains(c)) {
            System.out.print(c);
        }
    }
    System.out.println();
}

As for that happening within a string because of a character literal, I'm not sure that it's possible. Some tests:

• \\b (the backspace character) doesn't work
• (char)127 (the delete character) doesn't work

That said, if your passwords can have backslashes ( \\ ) in them, that can absolutely be a problem. \\ in Java is used to denote a special character, with the following character. The string "nnn" is just "nnn" , but "n\\nn" is

 n
 n

Because \\n represents a newline, the third n is lost.

There are many specialty characters denoted like this, but more importantly your passwords really can't have \\ in them without causing issues. Either you're getting an escape character if the following character if the following character with a backslash is legal (and \\1 actually is) , or it won't print if it's not legal.

Answer 2

Solving this same problem using Java 8:

    List<String> ignore = Arrays.asList("r", "2", "3");
    String text = "Hello world 1 2 3";
    text=toRemove.stream().map(toRem-> (Function<String,String>)s->s.replaceAll(toRem, "")).reduce(Function.identity(), Function::andThen).apply(text);
    System.out.println(text);

Output:

Hello wold 1