常用类练习提

package homework;
import java.util.Arrays;
//1.编程. 已知字符串："this is a test of java". 
//按要求执行以下操作：
//   (1) 统计该字符串中字母s出现的次数
//   (2) 取出子字符串"test"
//   (3) 将本字符串复制到一个字符数组Char[] str中.
//   (4) 将字符串中每个单词的第一个字母变成大写， 输出到控制台。
//   (5) 用两种方式实现该字符串的倒叙输出。(用StringBuffer和for循环方式分别实现)
//   (6) 将本字符串转换成一个字符串数组，要求每个数组元素都是一个有意义的额英文单词,并输出到控制台
public class Work2 {
	public static void main(String[] args) {
		String a = "this is a test of java";
		System.out.println(count(a));
		System.out.println(sub(a));
		System.out.println(change(a));
		dao(a);
		System.out.println();
		System.out.println(daoo(a));
		System.out.println(Arrays.toString(shuzu(a)));
	}
	public static int count(String aa){
		char[] b = aa.toCharArray();//将字符串抓换为字符数组
		int sum = 0;
		for (int i = 0; i < b.length; i++) {
			if (b[i] == 's') {
				sum++;
			}
		}
		return sum;
	}
	public static String sub(String aa){
		String s = aa.substring(10, 14);//字符串的截取
		return s;
	}
	public static char[] copy(String aa){
		char[] c = aa.toCharArray();
		return c;
	}
	public static char[] change(String aa){
		char []b = aa.toCharArray();
		b[0] = (char) (b[0] - 32);
		for (int i = 1; i < b.length; i++) {
			if (b[i] == ' ') {
				b[i + 1] = (char) (b[i + 1] - 32);
			}
		}
		return b;
	}
	public static void dao(String aa){
		char[] c = aa.toCharArray();
		for (int i = c.length - 1; i >= 0; i--) {
			System.out.print(c[i]);
		}
	}
    public static StringBuffer daoo(String aa){
    StringBuffer buffer = new StringBuffer(aa);//创建StringBuffer对象，进行字符串翻转
	StringBuffer str = buffer.reverse();
	return str;
    }
    public static String[] shuzu(String aa){
    	String str[] = aa.split(" ");//拆分字符串放置到字符串数组
    	return str;
    }
}