下面是从给定字符串中删除所有子字符串的实现

public static String deleteAll(String str, String pattern)
{
    for(int index = isSubstring(str, pattern); index != -1; index = isSubstring(str, pattern))
        str = deleteSubstring(str, pattern, index);

    return str;
}

public static String deleteSubstring(String str, String pattern, int index)
{
    int start_index = index;
    int end_index = start_index + pattern.length() - 1;
    int dest_index = 0;
    char[] result = new char[str.length()];


    for(int i = 0; i< str.length() - 1; i++)
        if(i < start_index || i > end_index)
            result[dest_index++] = str.charAt(i);

    return new String(result, 0, dest_index + 1);
}

isSubstring()方法的实现在这里

你应该看看StringBuilder/StringBuffer，它允许你删除，插入，替换指定偏移量的字符。

replace('regex', 'replacement');
replaceAll('regex', 'replacement');

在你的例子中，

String hi = "Hello World!"
String no_o = hi.replaceAll("o", "");

查看Apache StringUtils:

static String replace(String text, String searchString, String replacement) Replaces all occurrences of a String within another String. static String replace(String text, String searchString, String replacement, int max) Replaces a String with another String inside a larger String, for the first max values of the search String. static String replaceChars(String str, char searchChar, char replaceChar) Replaces all occurrences of a character in a String with another. static String replaceChars(String str, String searchChars, String replaceChars) Replaces multiple characters in a String in one go. static String replaceEach(String text, String[] searchList, String[] replacementList) Replaces all occurrences of Strings within another String. static String replaceEachRepeatedly(String text, String[] searchList, String[] replacementList) Replaces all occurrences of Strings within another String. static String replaceOnce(String text, String searchString, String replacement) Replaces a String with another String inside a larger String, once. static String replacePattern(String source, String regex, String replacement) Replaces each substring of the source String that matches the given regular expression with the given replacement using the Pattern.DOTALL option.

private static void replaceChar() {
    String str = "hello world";
    final String[] res = Arrays.stream(str.split(""))
            .filter(s -> !s.equalsIgnoreCase("o"))
            .toArray(String[]::new);
    System.out.println(String.join("", res));
}

如果你有一些复杂的逻辑来过滤字符，那就用另一种方法代替replace()。

如果你知道开始和结束索引，你可以使用它

string = string.substring(0, start_index) + string.substring(end_index, string.length());