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Java StringJoiner Java实用工具之StringJoiner详解

黄智霖-blog 人气:0
想了解Java实用工具之StringJoiner详解的相关内容吗,黄智霖-blog在本文为您仔细讲解Java StringJoiner的相关知识和一些Code实例,欢迎阅读和指正,我们先划重点:Java,StringJoiner,Java实用工具,下面大家一起来学习吧。

背景

在平时的业务开发中,我们可能会遇到字符串列表根据分隔符进行拼接的需求。比如:

输入:

数组:[“a”,“b”,“c”]分隔符:","

输出:

“a,b,c”

处理

通常我们可以使用StringBuilder根据下标位置决定是否需要添加分隔符以达到目的,比如:

public static void main(String[] args) {
        StringBuilder sb = new StringBuilder();
        String[] strings = new String[]{"a", "b", "c"};
        String delimiter = ",";
        for (int i = 0; i < strings.length; i++) {
            if (i != 0) {
                sb.append(delimiter);
            }
            sb.append(strings[i]);
        }
        System.out.println(sb.toString());
    }

或者:

public static void main(String[] args) {
        StringBuilder sb = new StringBuilder();
        String[] strings = new String[]{"a", "b", "c"};
        String delimiter = ",";
        int tmp = strings.length - 1;
        for (int i = 0; i < strings.length; i++) {
            sb.append(strings[i]);
            if (i != tmp) {
                sb.append(delimiter);
            }
        }
        System.out.println(sb.toString());
    }

但是每次遇到这种情况都去这样拼接很麻烦,而且如果使用迭代器,没有下标就不能使用这种方法。那么就每次append分隔符,最后再截断:

public static void main(String[] args) {
        StringBuilder sb = new StringBuilder();
        String[] strings = new String[]{"a", "b", "c"};
        String delimiter = ",";
        for (String str:strings) {
            sb.append(str).append(delimiter);
        }
        System.out.println(sb.substring(0,sb.length()-1));
    }

所以通常情况下,我们都会去扩展一个StringBuilder以提供分隔符组装的功能,博主平时是这样弄的:

public class MyStringBuilder {
    private StringBuilder stringBuilder;
    private String delimiter;

    public MyStringBuilder(String delimiter) {
        this.delimiter = delimiter;
    }

    public MyStringBuilder append(String item) {
        getStringBuilder().append(item);
        return this;
    }

    /**
     * 模拟的就是这个逻辑:
     * if(index != 0){
     *   append(delimiter);
     * }
     * append(str);
     *
     * @return
     */
    private StringBuilder getStringBuilder() {
        if (stringBuilder == null) {
            //相当于index==0,
            stringBuilder = new StringBuilder();
        } else {
            stringBuilder.append(delimiter);
        }
        return stringBuilder;
    }

    @Override
    public String toString() {
        return stringBuilder == null ? "" : stringBuilder.toString();
    }
}

  在初始化的时候指定分隔符,然后每次直接append就行了,由内部决定在何时添加分隔符。
  在JDK1.8之后,提供了一个StringJoiner类,提供了类似的功能,可以在初始化的时候指定分隔符和前缀后缀:

StringJoiner sj = new StringJoiner(",","(",")");
sj.add("a").add("b").add("c");
System.out.println(sj.toString());
//输出:(a,b,c)

博主大致看了一下StringJoiner的实现逻辑,很简单,和咱们扩展StringBuilder基本是一样的逻辑,另外加入了前缀后缀,然后多了一个merge的功能:

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;
    }
————————————————
版权声明:本文为CSDN博主「黄智霖-blog」的原创文章,遵循CC 4.0 BY-SA版权协议,转载请附上原文出处链接及本声明。
原文链接:https://blog.csdn.net/huangzhilin2015/article/details/115376792

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