Basic data type and String in Java

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    This is my first IT blog,written in English,as my first attempt. 

    To begin with,I would like to talk something about basic data type.There are 8 original kinds of type in Java,including byte,int,short,long,char,float,double and boolean.They can be divided into four catagories,which are as follows.

    First of all is integer type,including byte,int,short and long.One byte is eight bits,can express 256 integer values. Byte has simple,as a result of which,its range is from -128 to127.Second is float type,including float and double.Third is char type and the last one is boolean type,which only has two results:true or false.

    In addition,all these types can converse from each other.Byte→short→char→int→long→float→double is automatically conversion.Otherwise,we need converse them forcibly.Importantly,we need to pay attention to their range in case of overflow.

    Next,let's talk about String.There are many functions of String.I want to list several common examples.

    1、charAt(int index);  It can return the char value of index location.

    2、contains(CharSequence s); If s is contained,it will return true,otherwise,it will return false.

    3、equals(Object anobject); Compare two objects to judge whether they are the same.

    4、indexOf(String str); It returns the first index when str appears in the String ***.

    5、replace(char Oldchar,char Newchar);It will return a new string where newchar replace oldchar in the old string, 

    6、substring(int beginIndex,int endIndex);It will return a substring from beginIndex to endIndex.

    7、toCharArray();It will converse a string to a chararray.

    Last but not least,String has something sepcial.For example,str1==str2 is different from str1.equals(sr2) when creating str1 or str2 in different ways.One may be String str1 = "abc"; Another may be String str2 = new String("abc");It has something to do with value delivery and address delivery.

 

My homework today is calculating the frequency of each char in the string.Thinking that is very easy,but for my lack of coding practise, I meet lots of difficulties.But  God helps those who help themselves, I make it in the end.Here is my code.

 

     And there is another one.Their basic idea is the same.

 

   Now I want to share several bugs I can remember.

   1、数组从第一个字符开始遍历，找到相同的就计数+1，然后打印出来，结果比如说前面a打印过了，后面遇到a它再去遍历了一次。解决办法：遍历一次，删除那个字符，从剩下的新的字符串再去遍历。

   2、....Sorry i can only remember the latest bug,bugs before i should completely forget! I promise i will put bugs down later in case of review.  

 

 

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1 楼 xuyi1994 2013-07-06  

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