2018.7.28第一题作业答案 7个题

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 stub

String 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 stub

String 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="      	你好java	 ";

    String f1=s2.replace("你好", "我是");

    String f2=s2.trim();

    System.out.println(f2);

    }

 

}