java自动装箱拆箱_Java自动装箱

迈不过友情╰ 2023-02-28 08:44 243阅读 0赞

java自动装箱拆箱

Autoboxing in java was introduced in Java 1.5. Autoboxing and unboxing is a convenient way to auto transform primitive data type to it’s corresponding [java wrapper classes][] and vice versa.

Java中的自动装箱是Java 1.5中引入的。 自动装箱和取消装箱是一种将原始数据类型自动转换为对应的[Java包装器类][java wrapper classes]的便捷方法，反之亦然。

### Java自动装箱 **(****Autoboxing in Java****)** ###

Converting a primitive data type into an object of the corresponding [wrapper class][java wrapper classes] is called **autoboxing**. For example, converting int to Integer or converting long to Long object.

将原始数据类型转换为相应[包装器类][java wrapper classes]的对象称为**自动装箱** 。 例如，将int转换为Integer或将long转换为Long对象。

Java compiler applies autoboxing when a primitive value is:

当原始值是：Java编译器将应用自动装箱：

1.  Passed as a parameter to a method that expects an object of the corresponding wrapper class. For example a method with Integer argument can be called by passing int, java compiler will do the conversion of int to Integer.
    
    作为参数传递给需要相应包装类对象的方法。 例如，可以通过传递int来调用带有Integer参数的方法，java编译器会将int转换为Integer。
2.  Assigned to a variable of the corresponding wrapper class. For example, assigning a Long object to long variable.
    
    分配给相应包装器类的变量。 例如，将long对象分配给long变量。

### 用Java取消装箱 **(****Unboxing in Java****)** ###

Converting an object of a wrapper type to its corresponding primitive data type is called **unboxing**.

将包装器类型的对象转换为其对应的原始数据类型的过程称为**拆箱** 。

Java compiler applies unboxing when an object of a wrapper class is:

当包装器类的对象是：

1.  Passed as a parameter to a method that expects a value of the corresponding primitive type.
    
    作为参数传递给需要相应原始类型值的方法。
2.  Assigned to a variable of the corresponding primitive type.
    
    分配给相应原始类型的变量。

### Java自动装箱示例 **(****Java Autoboxing Example****)** ###

Here is a small java program showing examples of autoboxing and unboxing in java.

这是一个小型Java程序，显示了Java自动装箱和拆箱的示例。

package com.journaldev.util;
    
    import java.util.ArrayList;
    import java.util.List;
    
    public class AutoboxingUnboxing {
    
    	public static void main(String[] args) {
    		int i = 5;
    		long j = 105L;
    
    		// passed the int, will get converted to Integer object at Runtime using
    		// autoboxing in java
    		doSomething(i);
    
    		List<Long> list = new ArrayList<>();
    
    		// java autoboxing to add primitive type in collection classes
    		list.add(j);
    	}
    
    	private static void doSomething(Integer in) {
    		// unboxing in java, at runtime Integer.intValue() is called implicitly to
    		// return int
    		int j = in;
    
    		// java unboxing, Integer is passed where int is expected
    		doPrimitive(in);
    	}
    
    	private static void doPrimitive(int i) {
    
    	}
    }

Note: It’s not a good idea to rely on autoboxing always, sometimes it can cause compiler error that method is ambiguous when a method is overloaded. Please refer to below screenshot for a quick example.

注意：始终依赖自动装箱不是一个好主意，有时在方法重载时，它可能导致编译器错误，即方法不明确。 请参考以下屏幕截图以获取快速示例。

Read more at [this StackOverflow article][]. Also go through [java ambiguous method call error][].

在[此StackOverflow文章中][this StackOverflow article]阅读更多[内容][this StackOverflow article] 。 还要经历[java模棱两可的方法调用错误][java ambiguous method call error] 。

That’s all about autoboxing and unboxing in java. This feature is very helpful in reducing code size because we don’t have to convert primitive type to object explicitly.

这就是java中自动装箱和拆箱的全部内容。 此功能在减小代码大小方面非常有用，因为我们不必将原始类型显式转换为对象。

> 翻译自: [https://www.journaldev.com/1005/autoboxing-java][https_www.journaldev.com_1005_autoboxing-java]

java自动装箱拆箱

[java wrapper classes]: https://www.journaldev.com/1002/wrapper-class-in-java
[this StackOverflow article]: https://stackoverflow.com/questions/501412/why-does-autoboxing-make-some-calls-ambiguous-in-java
[java ambiguous method call error]: https://www.journaldev.com/9107/the-method-is-ambiguous-for-the-type-java-ambiguous-method-call-null-error
[https_www.journaldev.com_1005_autoboxing-java]: https://www.journaldev.com/1005/autoboxing-java