如何用星号替换 Java 字符串中的所有字符

Question

I want to replace all the characters in a Java String with * character. So it shouldn't matter what character it is, it should be replaced with a * .

I know there are heaps of examples there on internet but have not one that replaces every character and I have tried myself but no success.

Answer 1

Java 11 and later

str = "*".repeat(str.length());

Note: This replaces newlines \\n with * . If you want to preserve \\n , see solution below.

Java 10 and earlier

str = str.replaceAll(".", "*");

This preserves newlines.

To replace newlines with * as well in Java 10 and earlier, you can use:

str = str.replaceAll("(?s).", "*");

The (?s) doesn't match anything but activates DOTALL mode which makes . also match \\n .

Answer 2

Don't use regex at all, count the String length, and return the according number of stars.

Plain Java < 8 Version:

int len = str.length();
StringBuilder sb = new StringBuilder(len);
for(int i = =; i < len; i++){
    sb.append('*');
}
return sb.toString();

Plain Java >= 8 Version:

int len = str.length();
return IntStream.range(0, n).mapToObj(i -> "*").collect(Collectors.joining());

Using Guava :

return Strings.repeat("*", str.length());
// OR
return CharMatcher.ANY.replaceFrom(str, '*');

Using Commons / Lang :

return StringUtils.repeat("*", str.length());

Answer 3

System.out.println("foobar".replaceAll(".", "*"));

Answer 4

public String allStar(String s) {
    StringBuilder sb = new StringBuilder(s.length());
    for (int i = 0; i < s.length(); i++) {
        sb.append('*');
    }
    return sb.toString();
}

Answer 5

How abt creating a new string with the number of * = number of last string char?

StringBuffer bf = new StringBuffer();
for (int i = 0; i < source.length(); i++ ) {
    bf.append('*');
}

Answer 6

There may be other faster/better ways to do it, but you could just use a string buffer and a for-loop:

public String stringToAsterisk(String input) {
    if (input == null) return "";

    StringBuffer sb = new StringBuffer();
    for (int x = 0; x < input.length(); x++) {
        sb.append("*");
    }
    return sb.toString();
}

If your application is single threaded, you can use StringBuilder instead, but it's not thread safe.

I am not sure if this might be any faster:

public String stringToAsterisk(String input) {
    if (input == null) return "";

    int length = input.length();
    char[] chars = new char[length];
    while (length > 0) chars[--length] = "*";
    return new String(chars);
}

Answer 7

Without any external library and without your own loop, you can do:

String input = "Hello";
char[] ca = new char[input.length()];
Arrays.fill(ca, '*');
String output = new String(ca);

BTW, both Arrays.fill() and String(char []) are really fast.

Answer 8

Recursive method

String nCopies(String s, int n) {
    return n == 1 ? s.replaceFirst(".$", "") : nCopies(s + s, --n);
}

Answer 9

    String text = "Hello World";
    System.out.println( text.replaceAll( "[A-Za-z0-9]", "*" ) );

output : ***** *****