java 基礎資料類型

資料|資料類型

1.單一資料型別
邏輯類型  boolean
文本類型  char,String(特殊類型)
整數類型  byte,short,int,long
浮點類型  double,float

boolean  兩個值:true and false
char  16位無符號(不分正負的)Unicode字元 必須包含在單引號內('')
       eg:'\t' 表示一個定位字元
            '\u????' 表示一個特殊的Unicode字元 ????應嚴格按照4個16進位數進行替換.
String  不是一個簡單的資料類型 而是一個類(class) 它被用來表示字元序列.字元本身符合Unicode標準
         且上述char類型的反斜線符號適用於String.
         與c and c++ 不同,String不能用'\o'作為結束.(本來要寫'\零'的,可是它就是不顯示,沒招兒了,就用o來代替吧~~)
byte short int long
         在資料後面直接跟一個字母"L".L表示這是一個long型數值.在Java程式設計語言中L無論是大寫還是小寫都同樣有效,但由於小寫l與數字1容易混淆,因而,使用小寫不是一個明智的選擇.
                                           整型資料的長度和數值範圍
   ----------------------------------------------------------------------------------------------------------------------
        長度                                    資料類型                                  數值範圍
   ----------------------------------------------------------------------------------------------------------------------
        8 bits                                     byte                                   -2(7)~2(7)-1
        16 bits                                   short                                   -2(15)~2(15)-1
        32 bits                                   int                                      -2(31)~2(31)-1
        64 bits                                   long                                    -2(63)~2(63)-1
   ---------------------------------------------------------------------------------------------------------------------
float double  
          數值包含小數點或指數,或者在數字後面帶有字母F or f(float), D or d(double)
                                           浮點型資料的長度和數值範圍
   ----------------------------------------------------------------------------------------------------------------------
        長度                                    資料類型                                  數值範圍
   ----------------------------------------------------------------------------------------------------------------------
        32 bits                                   float                              1.401e-45~3.402e+38
        64 bits                                   long                              4.94e-324~1.79e+308d
   ----------------------------------------------------------------------------------------------------------------------

2.單一資料型別變數的聲明和賦值
public class Assign{
  public static void main(String[] args){
     int x,y;                                          //declare int variables
     float z=3.414f;                               //declare and assign float variable
     double w=3.1415;                          //declare and assign double variable
     boolean truth=true;                        //declare and assign boolean variable
     char c;                                           //declare character variable
     String str;                                       //declare String variable
     String str1="bye";                            //declare and assign String variable
  c='A';                                                //assign value to char variable
  str="Hi out there!";                             //assign value to String variable
  x=6;
  y=1000;                                            //assign values to int variable
  ...
  }
}

下面是一些非法賦值的語句:
y=3.1415926;                               //is not an int.Requires casting and decimal will be truncated
w=175,000;                                 //the comma symbol(,)cannot appear
truth=1;                                      //a common mistake made by ex- c/c++ programmers
z=3.14156;                                  //can't fit double into a Float