如何增加类Integer从另一个方法引用java中的值
package myintergertest;
/**
*
* @author Engineering
*/
public class Main {
/**
* @param args the command line arguments
*/
public static void main(String[] args) {
//this one does not increment
Integer n = new Integer(0);
System.out.println("n=" + n);
Increment(n);
System.out.println("n=" + n);
Increment(n);
System.out.println("n=" + n);
Increment(n);
System.out.println("n=" + n);
Increment(n);
//this one will increment
MyIntegerObj myInt = new MyIntegerObj(1);
Increment(myInt);
System.out.println("myint = " + myInt.get());
Increment(myInt);
System.out.println("myint = " + myInt.get());
Increment(myInt);
System.out.println("myint = " + myInt.get());
}
public static void Increment(Integer n) {
//NO. this doesn't work because a new reference is being assigned
//and references are passed by value in java
n++;
}
public static void Increment(MyIntegerObj n) {
//this works because we're still operating on the same object
//no new reference was assigned to n here.
n.plusplus(); //I didn't know how to implement a ++ operator...
}
}
所有这些的结果是n = 0。整数n是一个对象,因此通过引用传递,那么为什么增量不会反映在调用方法(main)中?我期望输出为n = 0 n = 1 n = 2等...
The result for all of those is n=0. Integer n is an object and therefore passed by reference, so why isn't the increment reflected back in the caller method (main)? I expected output to be n=0 n=1 n=2 etc...
更新:
注意我更新了上面的代码示例。如果我理解正确,Jon Skeet回答了为什么myInt会增加以及为什么n不会增加的问题。这是因为n正在获取在Increment方法中指定的新引用。但myInt没有被分配一个新的引用,因为它正在调用一个成员函数。
UPDATE: Notice I updated the code example above. If I'm understanding correctly, Jon Skeet answered the question of why myInt would increment and why n does not. It is because n is getting a new reference assigned in the Increment method. But myInt does NOT get assigned a new reference since it's calling a member function.
这听起来像我理解正确吗?
Does that sound like I understand correctly lol ?
不,对象不通过引用传递。参考文献通过价值传递 - 这是一个很大的不同。 Integer
是一个不可变类型,因此您无法更改方法中的值。
No, objects aren't passed by reference. References are passed by value - there's a big difference. Integer
is an immutable type, therefore you can't change the value within the method.
您的 n ++;
语句实际上是
n = Integer.valueOf(n.intValue() + 1);
因此,它为变量 n $ c赋予不同的值$ c> in
Increment
- 但由于Java 仅具有按值传递,因此不会影响 n
在调用方法中。
So, that assigns a different value to the variable n
in Increment
- but as Java only has pass-by-value, that doesn't affect the value of n
in the calling method.
编辑:回答你的更新:那是对的。据推测,您的MyIntegerObj类型是可变的,并在您调用 plusplus()
时更改其内部状态。哦,不要四处寻找如何实现运算符--Java不支持用户定义的运算符。
To answer your update: that's right. Presumably your "MyIntegerObj" type is mutable, and changes its internal state when you call plusplus()
. Oh, and don't bother looking around for how to implement an operator - Java doesn't support user-defined operators.