Description

1. For each of the code snippets below, revise the code so that we use fully qualified name (i.e., the dot ( . ) notation) to access the fields. For example, use this.a and X.b instead of just a and b . Now suppose that the following is invoked:
B b = new B();
b.f();
Sketch the content of the stack and heap at Line A. Java run-time stores static fields in a region of memory called metaspace. Sketch that as well where appropriate.
(a) class B { static int x = 0;
void f() {
A a = new A();
// Line A
}
static class A {
int y = 0;
A() {
y = x + 1;
}
}
} (b) class B { void f() { int x = 0;
class A { int y = 0;
A() {
y = x + 1;
}
}
A a = new A();
// Line A
}
} (c) class B { int x = 1;
void f() { int y = 2;
class A { void g() {
x = y;
}
}

A a = new A(); // Line A
a.g();
}
}
2. Consider the following implementation of a stack.
public class Stack<T> { private T head; private Stack<T> tail; private static final Stack<?> EMPTY_STACK = new Stack<>(null, null);
private Stack(T head, Stack<T> tail){
this.head = head; this.tail = tail;
}
public void push(T t){
this.tail = new Stack<T>(this.head, this.tail); this.head = t;
}
public void pop(){
if (this.head == null) {
throw new IllegalStateException(“Stack is empty”);
} this.head = this.tail.head; this.tail = this.tail.tail;
}
public T head(){
if (this.head == null) {
throw new IllegalStateException(“Stack is empty”);
} return head;
}
public boolean isEmpty(){
if (this.head == null) {
return true;
} else {
return false;
} }
public static <T> Stack<T> createNew(){
@SuppressWarnings(“unchecked”)
Stack<T> emptyStack = (Stack<T>) EMPTY_STACK; return emptyStack;
}
}
The push and pop operations on the stack change (or mutate) the stack. Here is an example of how the Stack class can be used. The example below pushes 1, 2, and 3 into the stack and pops them out in reverse order.

jshell> /open Stack.java jshell> Stack<Integer> s = Stack.createNew(); jshell> s.push(1); jshell> s.push(2); jshell> s.push(3); jshell> s.head();
$6 ==> 3
jshell> s.pop(); jshell> s.head();
$8 ==> 2
jshell> s.pop(); jshell> s.head(); $10 ==> 1 jshell> s.pop(); jshell>
Changetheimplementationof Stack tomakeitimmutable. Createanewclass ImmutableStack . Show how it can be used by pushing 1, 2, and 3 into the immutable stack and by popping 3, 2, and 1 out from the stack.