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工具类系列---【java8新特性-字符串拼接工具StringJoiner类】

前言:

StringJoiner是Java8新出的一个类,用于构造由分隔符分隔的字符序列,并可选择性地从提供的前缀开始和以提供的后缀结尾。省的我们开发人员再次通过StringBuffer或者StingBuilder拼接。

用法示例:

StringJoiner sj = new StringJoiner(":", "[", "]");
sj.add("hu").add("jun").add("wei");
String desiredString = sj.toString();

输出结果:

[hu:jun:wei]

源码分析:

 

public String toString() {
if (value == null) {
return emptyValue;//没有值将返回空值或者后续设置的空值
} else {
if (suffix.equals("")) {
return value.toString();//后缀为""直接返回字符串,不用添加
} else {
//后缀不为"",添加后缀,然后直接返回字符串,修改长度
int initialLength = value.length();
String result = value.append(suffix).toString();
// reset value to pre-append initialLength
value.setLength(initialLength);
return result;
}
}
}
初始化,先添加前缀,有了之后每次先添加间隔符,StringBuilder后续append字符串
public StringJoiner add(CharSequence newElement) {
prepareBuilder().append(newElement);
return this;
}
//合并StringJoiner,注意后面StringJoiner 的前缀就不要了,后面的appen进来
public StringJoiner merge(StringJoiner other) {
Objects.requireNonNull(other);
if (other.value != null) {
final int length = other.value.length();
// lock the length so that we can seize the data to be appended
// before initiate copying to avoid interference, especially when
// merge 'this'
StringBuilder builder = prepareBuilder();
builder.append(other.value, other.prefix.length(), length);
}
return this;
}
//初始化,先添加前缀,有了之后每次先添加间隔符
private StringBuilder prepareBuilder() {
if (value != null) {
value.append(delimiter);
} else {
value = new StringBuilder().append(prefix);
}
return value;
}

public int length() {
// Remember that we never actually append the suffix unless we return
// the full (present) value or some sub-string or length of it, so that
// we can add on more if we need to.
//不忘添加后缀的长度
return (value != null ? value.length() + suffix.length() :
emptyValue.length());
}
}

 

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