package tet;

public class kk {

    public static void main(String[] args) {

        //1.

        {

            String Stra = "123abc";

            //得到指定索引处的char值

            char ca = Stra.charAt(3);

            System.out.println("1:  "+ca);

        }

        //2. compareTo比较两个对象的差值，compareToIgnoreCase忽略大小写，返回值都为差值

        {

            String Stra = "abc";

            String Strb = "ABC";

            String Strc = "aBc";

            System.out.println("2:  "+Stra.compareTo(Strb));

            System.out.println("2:  "+Stra.compareToIgnoreCase(Strc));

        }

        //3. 指定字符串在最后一次出现的位置

        {

            String Stra = "hello world  haha hello";

            int i = Stra.lastIndexOf("haha");

            System.out.println("3:  "+i);

            System.out.println("3:  "+Stra.lastIndexOf("hello"));

        }

        //4. 删除字符串中的一个字符

        {    //减去hello中的o

            String Stra = "hello world  haha";

            String Strb = Stra.substring(0, 4)+Stra.substring(5);

            System.out.println("4:  "+Strb);

        }

        //5. 替换字符串,注意：是返回替换后的，本身不会替换

        {

            String Stra = "hello world  haha";

            Stra.replace("hehe", "haha");

            System.out.println("5:  "+Stra);

            String Strb = Stra.replace("haha", "hehe");

            System.out.println("5:  "+Strb);

        }

        //6. 查找字符串

        {

            String Stra = "hello world  haha";

            System.out.println("6:  "+Stra.indexOf("world"));

            System.out.println("6:  "+Stra.indexOf("worle"));

        }

        //7. 字符串分割

        {

            String Stra = "www-baidu-com";

            String[] suba;

            suba = Stra.split("-");

            for(String x : suba){

                System.out.println("7:  "+x);

            }

            String Strb = "xxx hhh  ccc";  //注意：ccc前面有两个空格，第一个会检测到，第二个不是的了

            String[] subb;

            subb = Strb.split(" ");

            for(String x : subb){

                System.out.println("7:  "+x);

            }

        }

        //8. 去掉前后空格

        {

            String Stra = "   hello   ";

            System.out.println("8:  "+Stra+Stra.length());

            String Strb = Stra.trim();

            System.out.println("8:  "+Strb+Strb.length());

        }

        //9. 大小写转换

        {

            String Stra = "hello";

            String Strb = "HELLO";

            String Strc = "HellO";

            System.out.println("9:  "+Stra.toUpperCase());  //小写转大写

            System.out.println("9:  "+Strb.toLowerCase());  //大写转小写

            System.out.println("9:  "+Strc.toUpperCase());  //有大写有小写的字符串也能转换

        }

        //10. 格式化字符串

        {

            int i=5;double d = 6.6;

            String Stra = String.format("haha=%d,hehe=%f",i,d);

            System.out.println("10: "+Stra);

        }

        //11. 连接字符串

        {

            String Stra = "hello";

            String Strb = Stra.concat("  hehe");

            System.out.println("11: "+Stra);

            System.out.println("11: "+Strb);

        }

        //12. 字符串性能测试

        {

            double current = System.currentTimeMillis();

            for(int i=0;i<500000;i++){

                String a = "hello";

            }

            double end = System.currentTimeMillis();

            System.out.println("12: 耗时="+(end-current)+"毫秒");  

            double current1 = System.currentTimeMillis();

            for(int i=0;i<500000;i++){

                String a = new String("haha");

            }

            double end1 = System.currentTimeMillis();

            System.out.println("12: 耗时="+(end1-current1)+"毫秒");

        }

    }

}

1:  a

2:  32

2:  0

3:  13

3:  18

4:  hell world  haha

5:  hello world  haha

5:  hello world  hehe

6:  6

6:  -1

7:  www

7:  baidu

7:  com

7:  xxx

7:  hhh

7:

7:  ccc

8:     hello   11

8:  hello5

9:  HELLO

9:  hello

9:  HELLO

10: haha=5,hehe=6.600000

11: hello

11: hello  hehe

12: 耗时=7.0毫秒

12: 耗时=25.0毫秒