Java实用工具之StringJoiner详解

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());
    }

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());
    }

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));
    }

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();
    }
}

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

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;
    }