java - NumberFormat Java 中的格式方法

Question

有人知道 this 的真正用途吗？方法？

format

public StringBuffer format(Object number, StringBuffer toAppendTo, FieldPosition pos)

Formats a number and appends the resulting text to the given string buffer. The number can be of any subclass of Number.

StringBuffer 如何与 FieldPosition 交互(整数/小数)。

简而言之，现实生活中的代码示例将非常有用。

Answer 1

格式化一个 long 值并打印出 long 整数部分的开始和结束索引:

    // Get a default NumberFormat instance.
    NumberFormat numForm = NumberFormat.getInstance();

    // Format some longs using the pattern supplied above.
    StringBuffer dest1 = new StringBuffer(24);
    StringBuffer dest2 = new StringBuffer(24);
    FieldPosition pos = new FieldPosition(NumberFormat.INTEGER_FIELD);

    dest1 = numForm.format(223423L, dest1, pos);
    System.out.println("dest1 = " + dest1);
    System.out.println("INTEGER portion is at: " + pos.getBeginIndex() +
        ", " + pos.getEndIndex());

    dest2 = numForm.format(64000L, dest2, pos);
    System.out.println("dest2 = " + dest2);
    System.out.println("INTEGER portion is at: " + pos.getBeginIndex() +
        ", " + pos.getEndIndex());

输出:

目标1 = 223,423

INTEGER 部分位于:0, 7

目标2 = 64,000

INTEGER 部分位于:0, 6