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

• 算術運算符

• 關係運算符

• 位運算符

• 邏輯運算符

• 賦值運算符

• 其它運算符

算術運算符：

算術運算符用於在數學表達式中，他們是在代數中使用的方法相同。下表列出了算術運算符：

假設整型變量A=10和變量B=20，則：

算術運算實例

運算符	描述	實例
+	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

關係運算符：

有下列由Java語言支持的關係運算符

假設變量A=10和變量B=20，則：

關係運算符實例

運算符	描述	實例
==	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.

按位運算符：

Java定義了幾個位運算符，它可以應用到整數類型，長型，整型，短整型，字符和字節。

位運算符作用於位，並執行逐位操作。假設當a =60和b= 13; 現在以二進製格式，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

下表列出了按位運算符：

假設整型變量A=60和變量B=13，則：

位運算實例

運算符	描述	實例
&	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

邏輯運算符：

下表列出了邏輯運算符：

假設布爾變量A=ture，變量B=false，那麼：

邏輯運算符實例

運算符	描述	實例
&&	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.

賦值運算符：

有下列由Java語言支持賦值操作符：

賦值運算符實例

運算符	描述	實例
=	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

其它運算符

Java 語言支持一些其他的運算符。

條件運算符 ( ? : ):

條件運算符也被稱為三元運算符。該運算符包括三個操作數，用於評估計算布爾表達式。此運算符的目標是確定哪些值應分配給該變量。可寫為：

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

下麵是例子：

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 : 30
Value of b is : 20

instanceof運算符：

這個操作符隻用於對象引用變量。操作檢查對象是否為特定類型（類類型或接口類型）。instanceof 運算符被寫為：

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

如果運算符的左側提到的變量的對象傳遞了IS-A檢查右側的類/接口類型，那麼結果將為 true。下麵是例子：

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兼容。下麵是一個例子：

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

優先級的Java操作符：

運算符優先級決定的條件在表達式中分組。這會影響一個表達式如何計算。某些運算符的優先級高於其它，例如，乘法運算符的優先級比加法運算高：

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

這裡，具有最高優先級的操作出現在表格上方，那些具有最低出現在底部。在表達式中，優先級較高的運算符將首先評估計算。

分類	運算符	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

下一步學的是什麼？

下一章會解釋有關Java編程的閉環控製。本章將介紹不同類型的循環以及如何將這些循環可以在Java程序開發和使用何種目的。