前几天偶然看到jdk1.8突然新增了一个类StringJoiner , 就研究了一下是怎么使用的, 以及看了下它的源码.
使用如下:
public static void main(String[] args) {
//间隔符是,
StringJoiner joiner1 = new StringJoiner(",");
joiner1.add("1").add("2").add("3");
System.out.println(joiner1.toString());
//1,2,3
//以[开头中间的间隔符是,以]结尾
StringJoiner joiner2 = new StringJoiner(",", "[", "]");
joiner2.add("1").add("2").add("3");
System.out.println(joiner2.toString());
//[1,2,3]
}
//我们先看下他的构造方法:
如果只有中间的一个分割字符, 则其左边和右边的字符都是空,
//前缀
private final String prefix;
//后缀
private final String delimiter;
//中间分隔符
private final String suffix;
public StringJoiner(CharSequence delimiter) {
this(delimiter, "", "");
}
public StringJoiner add(CharSequence newElement) {
prepareBuilder().append(newElement);
return this;
}
private StringBuilder prepareBuilder() {
if (value != null) {
value.append(delimiter);
} else {
value = new StringBuilder().append(prefix);
}
return value;
}
add方法, 首先是把值拼接一下前缀,再拼接一下中间的分隔符,再返回, 再继续拼接来的字符串.
@Override
public String toString() {
if (value == null) {
return emptyValue;
} else {
if (suffix.equals("")) {
return value.toString();
} else {
int initialLength = value.length();
String result = value.append(suffix).toString();
// reset value to pre-append initialLength
value.setLength(initialLength);
return result;
}
}
}
重写的toString方法,就是把整个StringBuilder转化为String了.
