Java私人學習筆記——第2章 資料類型和運算子

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2.2 資料類型2.2.1 Java資料類型 2.3 常用運算子

Java提供了一組運算子豐富的操縱變數。我們可以把所有的Java操作符為以下幾組：

• 算術運算子

• 關係運算子

• 位元運算符

• 邏輯運算子

• 賦值運算子

• 其它運算子

算術運算子：

算術運算子用於在數學運算式中，他們是在代數中使用的方法相同。下表列出了算術運算子：

假設整型變數A=10和變數B=20，則：

算術運算執行個體

運算子	描述	執行個體
+	Addition - Adds values on either side of the operator	A + B = 30
-	Subtraction - Subtracts right hand operand from left hand operand	A - B = -10
*	Multiplication - Multiplies values on either side of the operator	A * B = 200
/	Division - Divides left hand operand by right hand operand	B / A = 2
%	Modulus - Divides left hand operand by right hand operand and returns remainder	B % A = 0
++	Increment - Increases the value of operand by 1	B++ =21
--	Decrement - Decreases the value of operand by 1	B-- =19

關係運算子：

有下列由Java語言支援的關係運算子

假設變數A=10和變數B=20，則：

關係運算子執行個體

運算子	描述	執行個體
==	Checks if the values of two operands are equal or not, if yes then condition becomes true.	(A == B) is not true.
!=	Checks if the values of two operands are equal or not, if values are not equal then condition becomes true.	(A != B) is true.
>	Checks if the value of left operand is greater than the value of right operand, if yes then condition becomes true.	(A > B) is not true.
<	Checks if the value of left operand is less than the value of right operand, if yes then condition becomes true.	(A < B) is true.
>=	Checks if the value of left operand is greater than or equal to the value of right operand, if yes then condition becomes true.	(A >= B) is not true.
<=	Checks if the value of left operand is less than or equal to the value of right operand, if yes then condition becomes true.	(A <= B) is true.

按位元運算符：

Java定義了幾個位元運算符，它可以應用到整數類型，長型，整型，短整型，字元和位元組。

位元運算符作用於位，並執行逐位操作。假設當a =60和b= 13; 現在以二進位格式，他們將會如下：

a = 0011 1100

b = 0000 1101

-----------------

a&b = 0000 1100

a|b = 0011 1101

a^b = 0011 0001

~a  = 1100 0011

下表列出了按位元運算符：

假設整型變數A=60和變數B=13，則：

位元運算執行個體

運算子	描述	執行個體
&	Binary AND Operator copies a bit to the result if it exists in both operands.	(A & B) will give 12 which is 0000 1100
|	Binary OR Operator copies a bit if it exists in either operand.	(A | B) will give 61 which is 0011 1101
^	Binary XOR Operator copies the bit if it is set in one operand but not both.	(A ^ B) will give 49 which is 0011 0001
~	Binary Ones Complement Operator is unary and has the effect of ‘flipping‘ bits.	(~A ) will give -61 which is 1100 0011 in 2‘s complement form due to a signed binary number.
<<	Binary Left Shift Operator. The left operands value is moved left by the number of bits specified by the right operand.	A << 2 will give 240 which is 1111 0000
>>	Binary Right Shift Operator. The left operands value is moved right by the number of bits specified by the right operand.	A >> 2 will give 15 which is 1111
>>>	Shift right zero fill operator. The left operands value is moved right by the number of bits specified by the right operand and shifted values are filled up with zeros.	A >>>2 will give 15 which is 0000 1111

邏輯運算子：

下表列出了邏輯運算子：

假設布爾變數A=ture，變數B=false，那麼：

邏輯運算子執行個體

運算子	描述	執行個體
&&	Called Logical AND operator. If both the operands are non-zero, then the condition becomes true.	(A && B) is false.
||	Called Logical OR Operator. If any of the two operands are non-zero, then the condition becomes true.	(A || B) is true.
!	Called Logical NOT Operator. Use to reverses the logical state of its operand. If a condition is true then Logical NOT operator will make false.	!(A && B) is true.

賦值運算子：

有下列由Java語言支援賦值操作符：

賦值運算子執行個體

運算子	描述	執行個體
=	Simple assignment operator, Assigns values from right side operands to left side operand	C = A + B will assign value of A + B into C
+=	Add AND assignment operator, It adds right operand to the left operand and assign the result to left operand	C += A is equivalent to C = C + A
-=	Subtract AND assignment operator, It subtracts right operand from the left operand and assign the result to left operand	C -= A is equivalent to C = C - A
*=	Multiply AND assignment operator, It multiplies right operand with the left operand and assign the result to left operand	C *= A is equivalent to C = C * A
/=	Divide AND assignment operator, It divides left operand with the right operand and assign the result to left operand	C /= A is equivalent to C = C / A
%=	Modulus AND assignment operator, It takes modulus using two operands and assign the result to left operand	C %= A is equivalent to C = C % A
<<=	Left shift AND assignment operator	C <<= 2 is same as C = C << 2
>>=	Right shift AND assignment operator	C >>= 2 is same as C = C >> 2
&=	Bitwise AND assignment operator	C &= 2 is same as C = C & 2
^=	bitwise exclusive OR and assignment operator	C ^= 2 is same as C = C ^ 2
|=	bitwise inclusive OR and assignment operator	C |= 2 is same as C = C | 2

其它運算子

Java 語言支援一些其他的運算子。

條件運算子 ( ? : ):

條件運算子也被稱為三元運算子。該運算子包括三個運算元，用於評估計算布林運算式。此運算子的目標是確定哪些值應分配給該變數。可寫為：

variable x = (expression) ? value if true : value if false

下面是例子：

public class Test {   public static void main(String args[]){      int a , b;      a = 10;      b = (a == 1) ? 20: 30;      System.out.println( "Value of b is : " +  b );      b = (a == 10) ? 20: 30;      System.out.println( "Value of b is : " + b );   }}

這將產生以下結果：

Value of b is : 30Value of b is : 20

instanceof運算子：

這個操作符只用於對象引用變數。操作檢查對象是否為特定類型（類類型或介面類型）。instanceof 運算子被寫為：

( Object reference variable ) instanceof  (class/interface type)

如果運算子的左側提到的變數的對象傳遞了IS-A檢查右側的類/介面類型，那麼結果將為 true。下面是例子：

public class Test {   public static void main(String args[]){      String name = "James";      // following will return true since name is type of String      boolean result = name instanceof String;        System.out.println( result );   }}

這將產生以下結果：

true

這個操作符仍然會返回true，如果被比較的對象是分配在右側的類型相容。下面是一個例子：

class Vehicle {}public class Car extends Vehicle {   public static void main(String args[]){      Vehicle a = new Car();      boolean result =  a instanceof Car;      System.out.println( result );   }}

這將產生以下結果：

true

優先順序的Java操作符：

運算子優先順序決定的條件在運算式中分組。這會影響一個運算式如何計算。某些運算子的優先順序高於其它，例如，乘法運算子的優先順序比加法運算高：

例如x= 7+3* 2;這裡x被賦值13，而不是20，因為運算子*的優先順序高於+，所以它首先被乘以3 * 2，然後加7。

這裡，具有最高優先順序的操作出現在表格上方，那些具有最低出現在底部。在運算式中，優先順序較高的運算子將首先評估計算。

分類	運算子	關聯
Postfix	() [] . (dot operator)	Left to right
Unary	++ - - ! ~	Right to left
Multiplicative	* / %	Left to right
Additive	+ -	Left to right
Shift	>> >>> <<	Left to right
Relational	> >= < <=	Left to right
Equality	== !=	Left to right
Bitwise AND	&	Left to right
Bitwise XOR	^	Left to right
Bitwise OR	|	Left to right
Logical AND	&&	Left to right
Logical OR	||	Left to right
Conditional	?:	Right to left
Assignment	= += -= *= /= %= >>= <<= &= ^= |=	Right to left
Comma	,	Left to right

Java私人學習筆記——第2章 資料類型和運算子