java中StringBuffer的用法

2.StringBuffe

StringBuffer：String类同等的类，它允许字符串改变（原因见上一段所说）。Overall, this avoids creating many temporary （临时）strings, in other words, without StringBuffer, you must create many temporary strings.  StringBuffer的内部实现原理：马克-to-win，Every string buffer（缓存） has a capacity（容量）. As long as the length of the character sequence contained in the string buffer does not exceed（超过） the capacity, it is not necessary to allocate（分配） a new internal buffer array. If the internal buffer overflows（满后溢出）, it is automatically made larger.附带一句：从JDK5开始引入StringBuilder类，它是简易的StringBuffer，速度更快，但线程不安全

public class Test {

    public static void main(String[] args) {

        StringBuffer buffer;

        buffer = new StringBuffer();

        buffer.append("1");

        System.out.println(buffer);

        buffer.append("2");

        System.out.println(buffer);

    }

}

3.Arrays:

Arrays defined in java.util package

It gives a lots of static methods to manipulate（操纵） array.

int[] result = new int[k];

Arrays.sort(result);

import java.util.Arrays;

public class Test {

    public static void main(String[] args) {

        int[] result = { 4, 5, 2, 7, 8 };

        Arrays.sort(result);//当我们用到jdk自带的sort方法时，一下就排好序了，记得第一章，我们自己排序时，有多麻烦吗？

        for (int i = 0; i < result.length; i++) {

            System.out.println("" + result[i]);

        }

    }

}

更多请见：https://blog.csdn.net/qq_44639795/article/details/101552193