用+连接字符串总是个坏主意吗?

+

String word = "Hello";
word += " World!";

StringBuilder

StringBuilder sb = new StringBuilder();
for (My my : myList) {
    sb.append(my.getX());
}

string+=string

private String(String s1, String s2) {
    if (s1 == null) {
        s1 = "null";
    }
    if (s2 == null) {
        s2 = "null";
    }
    count = s1.count + s2.count;
    value = new char[count];
    offset = 0;
    System.arraycopy(s1.value, s1.offset, value, 0, s1.count);
    System.arraycopy(s2.value, s2.offset, value, s1.count, s2.count);
}

final void append0(String string) {
    if (string == null) {
        appendNull();
        return;
    }
    int adding = string.length();
    int newSize = count + adding;
    if (newSize > value.length) {
        enlargeBuffer(newSize);
    }
    string.getChars(0, adding, value, count);
    count = newSize;
}

string + string

public static String scat(String... vargs) {
    StringBuilder sb = new StringBuilder();

    for (String str : vargs)
        sb.append(str);

    return sb.toString();
}

String abcd = scat("a","b","c","d"); 

string.Concat();

public static String scat(Collection<?> vargs) {
    StringBuilder sb = new StringBuilder();

    for (Object str : vargs)
        sb.append(str);

    return sb.toString();
}

result = scat(myList)

+

String c = "a" + "b"

String result = "Scanning found " + Integer.toString(numberOfViruses) + " viruses";

StringBuilder