在方法中使用实例变量时的堆和堆栈（Java 内存）

Question

public class Main {
    private String sampleName= "Sample";
    public void show() {
        System.out.println(sampleName);
    }
}

I know "Sample" as a object locates in heap section, but Where is "sampleName" as a reference variable? if it locates in heap, whether in stack I have another reference with name "sampleName" that reference to "sampleName" in heap ?

Answer 1

I know "Sample" as a object locates in heap section

Correct.

but Where is "sampleName" as a reference variable?

In the Main object, which by definition is in the heap.

if it locates in heap, whether in stack I have another reference with name "sampleName" that reference to "sampleName" in heap

Yes, as a temporary for the argument to println() .

Answer 2

Your thread would only hold a reference to the enclosing Main object. It points to the Main object allocated in the heap. The sampleName reference is a field of the Main object, hence also on the heap, pointing to the String "Sample" , which is maintained in the java constant String pool (another section in the heap). There can't be a sampleName reference on the stack since it's a private field; otherwise, you would be able to access it in your code outside of the Main class, which is violating the java language semantics. If you defined the sampleName field to be public , and in your code you did

Main main = new Main();
String copyOfSampleName = main.sampleName;

Then you would have a String reference on your stack that is pointing, together with the original sampleName reference, to the String object in the constant pool.