How can I use a method to change a value?

Question

class Trial {
static void main() {
    int i = 0;
    change(i);
    System.out.println(i);
}
static void change(int n) {
    n = n + 2;
    }
}

Output I'm getting - 0 Output I want - 2

Please help me change my code.

Answer 1

Everything in Java is pass by value: http://www.javaranch.com/campfire/StoryPassBy.jsp

Try this instead:

class Trial {
    static void main() {
        int i = 0;
        i = change(i);
        System.out.println(i);
    }
    static int change(int n) {
        return n + 2;
    }
}

Edit

A parameter to a method is given a copy of the value. This value will either be a raw value (primitive) or an object reference (object).

For objects, a copy of the reference means you can change the state of an object within a method. What you cannot do is change the state having changed what the parameter is referring to.

Example 1:

class Person {
    private String name;
    public Person() {
    }

    public Person(String name) {
        this.name = name;
    }
    public String getName() {
        return this.name;
    }
    public void setName(final String name) {
        this.name = name;
    }
}

Person p = new Person("James");
changeName(p);
System.out.println(p.getName()); // This will output Changed
...
public void changeName(Person person) {
    person.setName("Changed");
}

Example 2:

Person p = new Person("James");
changeName(p);
System.out.println(p.getName()); // This will output James
...
public void changeName(Person person) {
    person = new Person(); // person is now referring to new object, not the one passed
    person.setName("Changed");
}