How Methods Work in Java

When you call a method in Java, the Java Virtual Machine (JVM) manages everything behind the scenes using a structure called the call stack. The call stack keeps track of every method call your program makes, making sure each method has its own space for parameters, return values, and local variables.

Method Calls and the Call Stack

• Each time you call a method, the JVM creates a new stack frame on the call stack;
• This stack frame holds the method's parameters, local variables, and the return address (where the program should continue after the method finishes);
• When the method finishes, its stack frame is removed, and the program continues from where it left off.

Parameters, Return Values, and Local Variables

• Parameters are the values you pass into a method. The JVM stores them in the new stack frame;
• Local variables declared inside the method also live in this stack frame, separate from variables in other methods;
• When a method returns a value, the JVM uses the stack frame to store the return value temporarily until it is passed back to the caller.

How Object References Are Passed

• In Java, when you pass an object to a method, you are actually passing a reference to that object, not the object itself;
• The reference (like an address) is copied into the method's stack frame, so both the caller and the method can access the same object in memory;
• Changes to the object's fields inside the method affect the original object, but reassigning the reference inside the method does not change the original reference outside the method.

Understanding how the JVM handles method calls helps you write better, more efficient Java programs and avoid common mistakes with variables and object references.