java中StringBuffer的用法

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
马克- to-win：马克 java社区：防盗版实名手机尾号： 73203。
本章源码

　

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);
    }
}

　

result is:

1
12

assignment: make a class called MyStringBuffer(char[] buf, initial size is 5, increment is 3, test program is you repeatedly store ordinary String,(the series is "abc","def","hlj") observe the effect.　




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]);
        }
    }
}

　

result is:

2
4
5
7
8