有没有办法在调用这些方法时避免使用构造函数？

Question

I have this code trying to modify the choice string by adding "wow" to the end of it. I am trying to use a custom class rather than just concatenating Strings because I want to be able to run other methods on it in the future as well.

for(String choice : commands) {
    count++;
    if(goAvailable.contains(choice)) {
        actionApnd("You went to " + new ModifyString(choice).append("wow") + ".");
        //System.err.print(choice + " ");
        break;
    } else if (count == commands.length) {
        actionApnd("Where did you want to go?");
    }

}

the ModifyString class (trimmed down):

public ModifyString(String str) {

    stringToReturn = str;
}

public String append(String toAppend) {

    stringToReturn += toAppend;

    return stringToReturn.trim();
}

I had this method in the ModifyString class and was using it instead of a constructor, but an error message told me I can't run append on the type String.

public static String string(String str) {

    stringToReturn = str;
    return stringToReturn.trim();
}

Answer 1

public static String string(String str) {

    stringToReturn = str;
    return stringToReturn.trim();
}

The issue is that stringToReturn is an instance field on ModifyString , meaning that it's associated with a specific instance of that class. There is no such instance in a static method.

It's unclear what you're trying to achieve, given that the return type is String : you could simply remove the first statement:

public static String string(String str) {
    return str.trim();
}

but then you may as well just invoke str.trim() directly.

Alternatively, you may have meant to return an instance of ModifyString :

public static ModifyString string(String str) {
    return new ModifyString(str.trim());
}

Note that string concatenation is a bad way to accumulate strings, because it requires copying the existing string in order to do the concatenation.

A better approach would be to use a StringBuilder , either directly, or wrapping it:

class ModifyString {
  private final StringBuilder sb;

  ModifyString(String str) {
    sb = new StringBuilder(str.trim());
  }

  ModifyString append(String str) {
    sb.append(str.trim());
    return this;
  }
}