Java 简明教程

Java - Basic Operators

Java operators 是用于对变量和值执行各种操作的符号。通过使用这些运算符，我们可以执行加法、减法、检查小于还是大于等操作。

Java operators are the symbols that are used to perform various operations on variables and values. By using these operators, we can perform operations like addition, subtraction, checking less than or greater than, etc.

Java 中有不同类型的运算符，我们已将它们列在下面 -

There are different types of operators in Java, we have listed them below −

Arithmetic Operators
Relational Operators
Bitwise Operators
Logical Operators
Assignment Operators
Misc Operators

Java Arithmetic Operators

算术运算符在数学表达式中使用的方式与其在代数中的使用方式相同。下表列出了算术运算符 −

Arithmetic operators are used in mathematical expressions in the same way that they are used in algebra. The following table lists the arithmetic operators −

假设整型变量 A 为 10，变量 B 为 20，那么 −

Assume integer variable A holds 10 and variable B holds 20, then −

Show Examples

Operator

Description

Example

+ (Addition)

Adds values on either side of the operator.

A + B will give 30

- (Subtraction)

Subtracts right-hand operand from left-hand operand.

A - B will give -10

* (Multiplication)

Multiplies values on either side of the operator.

A * B will give 200

/ (Division)

Divides left-hand operand by right-hand operand.

B / A will give 2

% (Modulus)

Divides left-hand operand by right-hand operand and returns remainder.

B % A will give 0

++ (Increment)

Increases the value of operand by 1.

B++ gives 21

— (Decrement)

Decreases the value of operand by 1.

B-- gives 19

Java Relational Operators

Java 语言支持以下关系运算符。

There are following relational operators supported by Java language.

假设变量 A 为 10，变量 B 为 20，那么 −

Assume variable A holds 10 and variable B holds 20, then −

Show Examples

Operator

Description

Example

== (equal to)

Checks if the values of two operands are equal or not, if yes then condition becomes true.

(A == B) is not true.

!= (not equal to)

Checks if the values of two operands are equal or not, if values are not equal then condition becomes true.

(A != B) is true.

> (greater than)

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.

< (less than)

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.

>= (greater than or equal to)

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.

⇐ (less than or equal to)

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.

Java Bitwise Operators

Java 定义了多个按位运算符，它们可以应用于整数类型 long、int、short、char 和 byte。

Java defines several bitwise operators, which can be applied to the integer types, long, int, short, char, and byte.

按位运算符对二进制位进行运算，并执行按位运算。假设 a = 60 且 b = 13；现在以二进制格式，它们如下所示：

Bitwise operator works on bits and performs bit-by-bit operation. Assume if a = 60 and b = 13; now in binary format they will be as follows −

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：

The following table lists the bitwise operators −

假设整数变量 A 保存 60 且变量 B 保存 13，则：

Assume integer variable A holds 60 and variable B holds 13 then −

Show Examples

Operator

Description

Example

& (bitwise and)

Binary AND Operator copies a bit to the result if it exists in both operands.

(A & B) will give 12 which is 0000 1100

(bitwise or)

Binary OR Operator copies a bit if it exists in either operand.

B) will give 61 which is 0011 1101

^ (bitwise XOR)

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

⁓ (bitwise compliment)

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.

<< (left shift)

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

>> (right shift)

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

>>> (zero fill right shift)

Java Logical Operators

下表列出了逻辑运算符：

The following table lists the logical operators −

假设布尔变量 A 为 true，变量 B 为 false，则：

Assume Boolean variables A holds true and variable B holds false, then −

Show Examples

Operator

Description

Example

&& (logical and)

Called Logical AND operator. If both the operands are non-zero, then the condition becomes true.

(A && B) is false

(logical or)

Called Logical OR Operator. If any of the two operands are non-zero, then the condition becomes true.

B) is true

! (logical not)

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.

The Assignment Operators

以下是 Java 语言支持的赋值运算符 −

Following are the assignment operators supported by Java language −

Show Examples

Operator

Description

Example

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.

= 2 is same as C = C

Java Miscellaneous Operators

Java 语言支持的其他几个运算符。

There are few other operators supported by Java Language.

Conditional Operator ( ? : )

条件运算符又称为 ternary operator。该运算符由三个操作数组成，用于评估布尔表达式。该运算符的目标是决定应将哪个值分配给变量。该运算符写为 −

Conditional operator is also known as the ternary operator. This operator consists of three operands and is used to evaluate Boolean expressions. The goal of the operator is to decide, which value should be assigned to the variable. The operator is written as −

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

以下是示例 −

Following is an example −

在这个示例中，我们创建了两个变量 a 和 b，并且使用 ternary operator 决定了 b 的值并打印出来了。

In this example, we’re creating two variables a and b and using ternary operator we’ve decided the values of b and printed it.

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 );
   }
}

Output

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

instanceof Operator

该运算符仅用于对象引用变量。该运算符检查对象是否为特定类型（类类型或接口类型）。instanceof 运算符写为 −

This operator is used only for object reference variables. The operator checks whether the object is of a particular type (class type or interface type). instanceof operator is written as −

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

如果运算符左侧变量引用的对象通过了右侧类/接口类型的 IS-A 检查，则结果将为 true。以下是示例 −

If the object referred by the variable on the left side of the operator passes the IS-A check for the class/interface type on the right side, then the result will be true. Following is an example −

Example

在此示例中，我们创建了一个 String 变量 name，然后使用 instanceof operator 检查 name 是否为 String。

In this example, we’re creating a String variable name and then using instanceof operator we’ve checking the name is of String or not.

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 );
   }
}

Output

true

如果要比较的对象与右侧的类型兼容，则此运算符仍将返回 true。以下是一个示例 −

This operator will still return true, if the object being compared is the assignment compatible with the type on the right. Following is one more example −

在此示例中，我们创建一个类的变量 a Vehicle，然后使用 instanceof operator 检查 name 是否为类型 Car。

In this example, we’re creating a variable a of class Vehicle and then using instanceof operator we’ve checking the name is of type Car or not.

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 );
   }
}

Output

true

Java Operators Precedence & Associativity

运算符优先级决定表达式中术语的分组。这会影响表达式的评估方式。某些运算符的优先级高于其他运算符；例如，乘法运算符的优先级高于加法运算符 −

Operator precedence determines the grouping of terms in an expression. This affects how an expression is evaluated. Certain operators have higher precedence than others; for example, the multiplication operator has higher precedence than the addition operator −

例如，x = 7 + 3 * 2；此处 x 分配为 13，而不是 20，因为运算符 * 的优先级高于 +，因此它首先与 3 * 2 相乘，然后加到 7 中。

For example, x = 7 + 3 * 2; here x is assigned 13, not 20 because operator * has higher precedence than +, so it first gets multiplied with 3 * 2 and then adds into 7.

此处，优先级最高的运算符显示在表顶部，优先级最低的运算符显示在表底部。在表达式中，将首先评估优先级较高的运算符。

Here, operators with the highest precedence appear at the top of the table, those with the lowest appear at the bottom. Within an expression, higher precedence operators will be evaluated first.