StringJoiner是JDK1.8新出的一個類，用于拼接字串時加入分隔符、前綴、后綴，不需要手動拼接這些與業務無關的符號，也省去處理邊界問題的麻煩，
使用說明
例子：將陣列中的元素拼接成以","分割的字串
String[] strings = new String[]{"a", "b", "c"};
拼接結果：a,b,c使用StringJoiner之前
public static void main(String[] args) {
String[] strings = new String[]{"a", "b", "c"};
StringBuilder sb = new StringBuilder();
for (String s : strings) {
// 需要在每一次拼接后面加","
sb.append(s).append(",");
}
// 拼接完后還需要將最后一個分隔符","去掉
String substring = sb.substring(0, sb.length() - 1);
System.out.println(substring);
}使用StringJoiner之后
public static void main(String[] args) {
String[] strings = new String[]{"a", "b", "c"};
// 構造方法引數是分隔符","每次拼接字串自動加上分隔符
StringJoiner sj = new StringJoiner(",");
for (String s : strings) {
// 直接拼接字串，無需處理分隔符和邊界問題
sj.add(s);
}
System.out.println(sj);
}StringJoiner介紹
StringJoiner有兩個構造方法：
一個引數的構造方法，構造一個以delimiter為分隔符的StringJoiner，每次拼接字串自動加上delimiter分隔符
public StringJoiner(CharSequence delimiter) {
this(delimiter, "", "");
}三個引數的構造方法，構造一個以delimiter為分隔符的StringJoiner，并且在最終的結果字串上拼接prefix前綴和suffix后綴，
public StringJoiner(CharSequence delimiter,
CharSequence prefix,
CharSequence suffix) {
Objects.requireNonNull(prefix, "The prefix must not be null");
Objects.requireNonNull(delimiter, "The delimiter must not be null");
Objects.requireNonNull(suffix, "The suffix must not be null");
// make defensive copies of arguments
this.prefix = prefix.toString();
this.delimiter = delimiter.toString();
this.suffix = suffix.toString();
this.emptyValue = this.prefix + this.suffix;
}add方法
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;
}最終是呼叫的StringBuilder的append方法
public StringBuilder append(CharSequence s) {
super.append(s);
return this;
}
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標籤：java
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