Java 中的等式(==)运算符，示例
原文:https://www . geesforgeks . org/equality-operator-in-Java-with-examples/
==运算符是 Java 中 关系运算符的一种，用于检查等式关系。它在比较后返回一个布尔结果，广泛用于循环语句以及条件 if-else 语句。
语法:
LHS value == RHS value
但是，在比较这些值时，通常会出现三种情况:
- 案例 1:当 LHS 和 RHS 值都是原始值时 这是案例中最简单的。由于原始数据存储在堆栈存储器中，在这种情况下，从堆栈存储器中获取双方的实际值并进行比较。如果两者相等，则返回 true，否则返回 false。
语法:
Actual value == Actual value
示例:
// Java program for using == operator
import java.io.*;
public class GFG {
public static void main(String[] args)
{
// Declaring primitive values
int a = 4;
int b = 4;
int c = 5;
// Comparing a and b using == operator
System.out.println("Are " + a
+ " and " + b
+ " equal? "
+ (a == b));
// Comparing b and c using == operator
System.out.println("Are " + b
+ " and " + c
+ " equal? "
+ (b == c));
}
}
Output:
Are 4 and 4 equal? true
Are 4 and 5 equal? false
-
Case 2: When one of LHS and RHS value is a primitive and the other is reference In this scenario, for the primitive side, the actual value is taken for comparison from the stack memory. But for the reference side, when an array is declared and initialized, the data is stored in the heap memory and the reference pointer in the stack memory. So all that is in the stack memory is the memory address.
语法:
```java Actual value == Address value OR Address value == Actual value
```
因此，当比较基元值和引用值时，程序不会编译并抛出一个错误:
Java 代码编译错误:-
```java prog.java:20: error: incomparable types: int and int[] + (a == b)); ^ 1 error
```
这是因为原语端的值很容易从堆栈内存中获取，但对于引用端，该值无法获取，因为该值位于堆内存中。因此出现了错误。
示例:
```java // Java program for using == operator
import java.io.*;
public class GFG { public static void main(String[] args) {
// Declaring primitive value int a = 4;
// Declaring reference value int[] b = { 1, 2, 3, 4 };
// Comparing a and b using == operator System.out.println("Are " + a + " and " + b + " equal? " + (a == b)); } } ```
- Case 3: When both of the LHS and RHS value are reference In this scenario, for both the sides, when an array is declared and initialized, the data is stored in the heap memory and the reference pointer in the stack memory. So both the variables, their address is checked. If both the variables point to the same memory address, then this operator returns true. Else it returns false.
语法:
```java Address value == Address value
```
示例:
```java // Java program for using == operator
import java.io.*;
public class GFG { public static void main(String[] args) {
// Declaring reference value int[] a = { 1, 2, 3, 4 }; int[] b = { 1, 2, 3, 4 }; int[] c = b;
// Comparing a and b using == operator // Though they both have the same value // the output will be false because // they both have a different address in the memory System.out.println("Are " + a + " and " + b + " equal? " + (a == b));
// Comparing b and c using == operator // Though they both have the same value // the output will be true because // they both have same address in the memory System.out.println("Are " + b + " and " + c + " equal? " + (b == c)); } } ```
Output:
```java Are [I@232204a1 and [I@4aa298b7 equal? false Are [I@4aa298b7 and [I@4aa298b7 equal? true
```
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