public class zuoye01 {//boolean isEmpty(): 判断字符串是不是空串,如果是空的就返回true     public static void main(String[] args) {       // TODO Auto-generated method stub       String str="";       boolean b=str.isEmpty();       System.out.println(b);       }       public boolean isEmpty(){       zuoye01 str = null;       if(str.isEmpty()) {           return true;           }else{           return false;           }        }       }

//char charAt(int index): 返回索引上的字符public class zuoye02 {      public static void main(String args[]) {            String a = "adsadasdddd";            char b = a.charAt(8);            System.out.println(b);        } }

//String toLowerCase(): 字符串转成小写public class zuoye03 {     public static void main(String[] args) {       // TODO Auto-generated method stubString s="ABCDEFG";String f=s.toLowerCase();System.out.println(f);    } }

//String toUpperCase(): 字符串转成大写public class zuoye04 {     public static void main(String[] args) {       // TODO Auto-generated method stubString s="abcdefg";String f=s.toUpperCase();System.out.println(f);    } }

//String repalce(char oldChar, char newChar): 将字符串中的老字符,替换为新字符public class zuoye05 {    public static void main(String[] args){        String s="你好java";        String f=s.replace('你', '我');                System.out.println(f);            }}

//String repalce(String old, String newstr): 将字符串中的老字符串,替换为新字符串public class zuoye06 {    public static void main(String[] args) {       String s2="你好java";    String f1=s2.replace("你好", "我是");    System.out.println(f1);    } }

//String trim(): 去掉字符串两端空格public class zuoye07 {         public static void main(String[] args) {    String s="你好java";    String f=s.replace('你', '我');    System.out.println(f);    String s2="      \t你好java\t ";    String f1=s2.replace("你好", "我是");    String f2=s2.trim();    System.out.println(f2);    } }