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Java基本运算符

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。