Android topics — 13: אותו חוזה, שני מבני נתונים

package com.example.topics;

import java.util.Locale;
import java.util.Objects;

/** An immutable book whose identity is its normalized code. */
public final class Book {
    public final String code;
    public final String title;

    public Book(String code, String title) {
        if (code == null || code.trim().isEmpty()) {
            throw new IllegalArgumentException("Book code is required");
        }
        this.code = code.trim().toUpperCase(Locale.ROOT);
        this.title = Objects.requireNonNull(title, "title");
    }

    @Override
    public boolean equals(Object other) {
        if (this == other) return true;
        if (!(other instanceof Book)) return false;
        return code.equals(((Book) other).code);
    }

    @Override
    public int hashCode() {
        return code.hashCode();
    }
}

package com.example.topics;

/** Operations shared by catalogs with different storage structures. */
public interface Catalog<T> {
    void add(T item);
    boolean contains(T item);
    int size();
}

package com.example.topics;

/** A duplicate is a recoverable user action, not a crash. */
public final class DuplicateItemException extends IllegalArgumentException {
    public DuplicateItemException() {
        super("This book code already exists");
    }
}

package com.example.topics;

import java.util.Objects;

/** Shares the add contract while leaving storage to subclasses. */
public abstract class AbstractCatalog<T> implements Catalog<T> {
    @Override
    public final void add(T item) {
        Objects.requireNonNull(item, "item");
        if (contains(item)) {
            throw new DuplicateItemException();
        }
        insert(item);
    }

    protected abstract void insert(T item);
}

package com.example.topics;

import java.util.ArrayList;
import java.util.List;
import java.util.Objects;

/** Linear search; lastChecks makes the work visible. */
public final class ListCatalog<T> extends AbstractCatalog<T> {
    private final List<T> items = new ArrayList<>();
    private int lastChecks;

    @Override
    public boolean contains(T item) {
        lastChecks = 0;
        for (T candidate : items) {
            lastChecks++;
            if (Objects.equals(candidate, item)) return true;
        }
        return false;
    }

    @Override
    protected void insert(T item) {
        items.add(item);
    }

    @Override
    public int size() {
        return items.size();
    }

    public int getLastChecks() {
        return lastChecks;
    }
}

package com.example.topics;

import java.util.HashSet;
import java.util.Set;

/** Hash-based membership uses Book.equals and Book.hashCode. */
public final class SetCatalog<T> extends AbstractCatalog<T> {
    private final Set<T> items = new HashSet<>();

    @Override
    public boolean contains(T item) {
        return items.contains(item);
    }

    @Override
    protected void insert(T item) {
        items.add(item);
    }

    @Override
    public int size() {
        return items.size();
    }
}

package com.example.topics;

import org.junit.Test;
import static org.junit.Assert.*;

public final class CatalogTest {
    @Test
    public void normalizedCodeDefinesEqualityAndHash() {
        Book first = new Book(" b-40 ", "First title");
        Book sameCode = new Book("B-40", "Different title");
        assertEquals(first, sameCode);
        assertEquals(first.hashCode(), sameCode.hashCode());
    }

    @Test
    public void listAndSetAgreeButListScansToLastItem() {
        ListCatalog<Book> list = new ListCatalog<>();
        SetCatalog<Book> set = new SetCatalog<>();
        for (int number = 1; number <= 40; number++) {
            Book book = new Book("B-" + number, "Book " + number);
            list.add(book);
            set.add(book);
        }
        Book last = new Book("b-40", "Lookup");
        assertTrue(list.contains(last));
        assertEquals(40, list.getLastChecks());
        assertTrue(set.contains(last));
        assertFalse(set.contains(new Book("B-99", "Missing")));
    }

    @Test
    public void duplicateAndBlankCodeAreRejectedWithoutChangingSize() {
        Catalog<Book> catalog = new SetCatalog<>();
        catalog.add(new Book("B-7", "Original"));
        try {
            catalog.add(new Book(" b-7 ", "Duplicate"));
            fail("DuplicateItemException expected");
        } catch (DuplicateItemException expected) {
            assertEquals(1, catalog.size());
        }
        try {
            new Book("  ", "Invalid");
            fail("IllegalArgumentException expected");
        } catch (IllegalArgumentException expected) {
            assertEquals(1, catalog.size());
        }
    }
}

private final ListCatalog<Book> listCatalog = new ListCatalog<>();
private final SetCatalog<Book> setCatalog = new SetCatalog<>();

for (int number = 1; number <= 40; number++) {
    String code = String.format(Locale.ROOT, "B-%02d", number);
    Book book = new Book(code, "Book " + number);
    listCatalog.add(book);
    setCatalog.add(book);
}
binding.addBook.setOnClickListener(view -> addBook());
binding.findBook.setOnClickListener(view -> findBook());

private void addBook() {
    try {
        Book book = new Book(binding.bookCode.getText().toString(), "Student book");
        listCatalog.add(book);
        setCatalog.add(book);
        binding.result.setText(getString(R.string.added, book.code, listCatalog.size()));
    } catch (DuplicateItemException duplicate) {
        binding.result.setText(R.string.duplicate_book);
    } catch (IllegalArgumentException invalid) {
        binding.result.setText(R.string.code_required);
    }
}

private void findBook() {
    try {
        Book query = new Book(binding.bookCode.getText().toString(), "Lookup");
        boolean inList = listCatalog.contains(query);
        int checks = listCatalog.getLastChecks();
        boolean inSet = setCatalog.contains(query);
        binding.result.setText(getString(R.string.lookup_result, query.code,
                inList ? getString(R.string.yes) : getString(R.string.no), checks,
                inSet ? getString(R.string.yes) : getString(R.string.no)));
    } catch (IllegalArgumentException invalid) {
        binding.result.setText(R.string.code_required);
    }
}