Java Pass Values and Return Results

Understand the idea

Reassigning a parameter does not reassign the caller’s variable. Mutating a shared object is different: the reference was copied, but the object was not cloned. Return a value when you want the caller to replace its local result explicitly. Keep parameter names and order clear because several parameters with the same type can be accidentally swapped without a compile error.

Run it locally

Use a local JDK 21 or newer. Save the complete example as Main.java in a separate lab folder, then compile and run it with the commands below. Java examples do not run in Bhylu’s browser playground. The -ea option enables assertion checks used by some lessons.

JDK and terminal setup

javac --release 21 -encoding UTF-8 -d out Main.java
java -ea -cp out Main

A worked example

public class Main {
    static int addOne(int value) { return value + 1; }
    static void appendDay(StringBuilder value) { value.append(" Sunday"); }

    public static void main(String[] args) {
        int seats = 5;
        System.out.println(addOne(seats));
        System.out.println(seats);
        StringBuilder label = new StringBuilder("Lab");
        appendDay(label);
        System.out.println(label);
    }
}

Expected output

6
5
Lab Sunday

The first helper returns a new primitive result while seats remains five. The second helper mutates the builder reached by the copied reference, so the caller observes the appended day. Neither call changes Java into a pass-by-reference language. The distinction is between copying a reference value and copying an object’s state.