Java使用方法添加到整数

Question

I am having trouble with a relatively simple problem: I am trying to use a method from another class to add to an integer in my main class but the value of my integer is not increasing, the value stays the same, this is what the code looks like:

public class prog{

/**
 * @param args
 * @throws MidiUnavailableException 
 */

public static void main(String[] args) {
int num = 11;
thing.add(num);
System.out.println(num);
}
}

and the class 'thing' being:

public class chords2 {

static void add(int val){
    val = val+9;

}

}

any tips on how to get this to work is most appreciated

Answer 1

In Java, int is passed by value. If you want to add you should return the value and reassign it.

static int add(int val){
    return val+9;
}

Then, to call it,

int num = 11;
num = thing.add(num);

Answer 2

What happens is that Java is always pass-by-value . So, in your example, if you modify the integer val inside the method, it won't have effect outside.

What can you do?

You can declare your method to return an integer , then you assign the result to the variable you want:

static int add(int val){
    return val + 9;    
}

and when you call it:

int num = 11;
num = SomeClass.add(num); // assign the result to 'num'

Answer 3

你应该在你的thing类中有一个私有的int val，否则在你的add（）方法中添加“return”语句并在返回的调用位置设置返回值。