你可以使用

String helloWorld = "Hello World";
String target = "e";
String replacement = "";
String replacedString = helloWorld.replace(target, replacement);

The answer is = Hllo World

或者你可以使用正则表达式

String original = "Java is one of best languages. OOP can be used in Java";
String regexTarget = "\\bJava\\b";
String replacedWord = original.replaceAll(regexTarget, "Python");

The answer is = Python is one of best languages. OOP can be used in Python

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。

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()。

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

你也可以使用Substring替换现有的字符串:

var str = "abc awwwa";
var Index = str.indexOf('awwwa');
str = str.substring(0, Index);

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

在你的例子中，

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