Java StringBuilder的长度，setLength，容量和ensureCapacity方法。

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public class Main 

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{

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   public static void main(String[] args)

   /*

    from 时   代    Java - nowjava.com 

   */

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   {

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      StringBuilder buffer = new StringBuilder("Hello, how are you?");

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      System.out.printf("buffer = %s\nlength = %d\ncapacity = %d\n\n",

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         buffer.toString(), buffer.length(), buffer.capacity());

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      buffer.ensureCapacity(75);

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      System.out.printf("New capacity = %d\n\n", buffer.capacity());

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      buffer.setLength(10);

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