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Java基本運算符

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。