Java提供了一组运算符丰富的操纵变量。我们可以把所有的Java操作符为以下几组：

• 算术运算符

• 关系运算符

• 位运算符

• 逻辑运算符

• 赋值运算符

• 其它运算符

算术运算符：

算术运算符用于在数学表达式中，他们是在代数中使用的方法相同。下表列出了算术运算符：

假设整型变量A=10和变量B=20，则：

算术运算实例

运算符	描述	实例
+	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

关系运算符：

有下列由Java语言支持的关系运算符

假设变量A=10和变量B=20，则：

关系运算符实例

运算符	描述	实例
==	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.

按位运算符：

Java定义了几个位运算符，它可以应用到整数类型，长型，整型，短整型，字符和字节。

位运算符作用于位，并执行逐位操作。假设当a =60和b= 13; 现在以二进制格式，他们将会如下：

a = 0011 1100

b = 0000 1101

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

a&b = 0000 1100

a|b = 0011 1101

a^b = 0011 0001

~a  = 1100 0011

下表列出了按位运算符：

假设整型变量A=60和变量B=13，则：

位运算实例

运算符	描述	实例
&	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

逻辑运算符：

下表列出了逻辑运算符：

假设布尔变量A=ture，变量B=false，那么：

逻辑运算符实例

运算符	描述	实例
&&	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.

赋值运算符：

有下列由Java语言支持赋值操作符：

赋值运算符实例

运算符	描述	实例
=	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

其它运算符

Java 语言支持一些其他的运算符。

条件运算符 ( ? : ):

条件运算符也被称为三元运算符。该运算符包括三个操作数，用于评估计算布尔表达式。此运算符的目标是确定哪些值应分配给该变量。可写为：

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 );
   }
}

这将产生以下结果：

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

instanceof运算符：

这个操作符只用于对象引用变量。操作检查对象是否为特定类型（类类型或接口类型）。instanceof 运算符被写为：

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

如果运算符的左侧提到的变量的对象传递了IS-A检查右侧的类/接口类型，那么结果将为 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 );
   }
}

这将产生以下结果：

true

这个操作符仍然会返回true，如果被比较的对象是分配在右侧的类型兼容。下面是一个例子：

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 );
   }
}

这将产生以下结果：

true

优先级的Java操作符：

运算符优先级决定的条件在表达式中分组。这会影响一个表达式如何计算。某些运算符的优先级高于其它，例如，乘法运算符的优先级比加法运算高：

例如x= 7+3* 2;这里x被赋值13，而不是20，因为运算符*的优先级高于+，所以它首先被乘以3 * 2，然后加7。

这里，具有最高优先级的操作出现在表格上方，那些具有最低出现在底部。在表达式中，优先级较高的运算符将首先评估计算。

分类	运算符	关联
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

下一步学的是什么？

下一章会解释有关Java编程的闭环控制。本章将介绍不同类型的循环以及如何将这些循环可以在Java程序开发和使用何种目的。