Classes, Objects, and `new`

import java.util.*;

public class RegistryV2 {

    // TODO: a Unit class holding name, id, readiness and active
    static class Unit {
    }

    // The same five units as Section 4.1:
    //   Atlas 101 88.5 true, Beacon 102 42.0 true, Cipher 103 95.5 false,
    //   Drift 104 61.0 true, Ember 105 73.5 true
    static Unit[] roster() { return new Unit[0]; }  // TODO

    static Unit highestReadiness(Unit[] units) { return null; }  // TODO
    static Unit findById(Unit[] units, int id) { return null; }  // TODO

    // Sort by readiness, highest first. Return a NEW array.
    static Unit[] sortedByReadinessDescending(Unit[] units) { return units; }  // TODO

    // How many arrays does one swap have to touch now?
    static int arraysNeededToSort() { return 4; }  // TODO

    public static void main(String[] args) {
        // TODO: print the roster, sorted by readiness
    }
}

public class Drawing {

    static class Address {
        String city;
        Address(String city) { this.city = city; }
    }

    static class Student {
        String name;
        int age;
        Address address;
    }

    static Student make(String name, int age, String city) { return null; }  // TODO

    // What does a brand new Student actually contain? Predict all three.
    static boolean freshStudentHasAddress() { return true; }  // TODO
    static String  freshStudentName()       { return ""; }    // TODO
    static int     freshStudentAge()        { return -1; }    // TODO

    // Assign one Student to another, change the second, and report on the first.
    static boolean assignmentSharesTheObject() { return false; }  // TODO

    // Copy name, age and address ONE AT A TIME into a new Student, then change
    // the city through the copy. Did the original change too?
    static boolean fieldCopyStillSharesAddress() { return false; }  // TODO

    // How many objects does each of these create?
    static int objectsCreatedBy(String what) { return 0; }  // TODO

    public static void main(String[] args) {
        // TODO: draw the stack and the heap for two students on paper first
    }
}

public class Behaviour {

    static class Rectangle {
        double width;
        double height;

        Rectangle(double width, double height) {
            this.width = width;
            this.height = height;
        }

        // TODO: move the four methods in here. They take NO Rectangle argument.
        //   double area()
        //   double perimeter()
        //   boolean isSquare()
        //   String describe()   returns something containing the area and isSquare
        //   void scale(double factor)  multiplies both sides
    }

    static Rectangle make(double w, double h) { return null; }  // TODO

    // How many arguments did area need before, and how many now?
    static int argumentsNeededBefore() { return 0; }  // TODO
    static int argumentsNeededNow()    { return 1; }  // TODO

    public static void main(String[] args) {
        // TODO: build a rectangle, describe it, scale it, describe it again
    }
}

public class Overhead {

    static class Boxed { int value; Boxed(int v) { value = v; } }

    static Object keep;   // hold a live reference while measuring

    static long usedBytes() { return 0; }  // TODO

    static long primitiveArrayBytes(int n) { return 0; }  // TODO: an int[n]
    static long objectArrayBytes(int n)    { return 0; }  // TODO: a Boxed[n], all filled

    // MODEL FOR THIS EXERCISE ONLY: 64-bit HotSpot, compressed references,
    // 12-byte headers, 8-byte object alignment. Other configurations differ.
    static int headerBytes()       { return 0; }  // TODO: the model's header
    static int bytesPerPrimitive() { return 0; }  // TODO
    static int bytesPerObject()    { return 0; }  // TODO: header + int, padded to a multiple of 8

    static long expectedObjectBytes(int n) { return 0; }  // TODO: objects plus the reference array

    public static void main(String[] args) {
        // TODO: measure both at 2,000,000 and compare
        // TODO: run with -Xms2g -Xmx2g so the heap is not resizing under you
    }
}