OOP Lab 4

This lab includes 5 Problems on Strings, Interfaces, and Packages. We count them as Problem 8 to 12 in continuation of Lab 3.

Each problem provides:

• Skeleton Java classes with TODOs (do not change method signatures).
• A self‑checking test that prints PASS/FAIL.
• A tiny in‑house Assert (no external libraries).

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How to Compile & Run (packages)

From the repository root:

# Compile everything into an 'out' folder
javac -d out $(find src -name "*.java")

# Run any test by its fully‑qualified class name:
java -cp out edu.lab.tests.Problem8Test
java -cp out edu.lab.tests.Problem9Test
java -cp out edu.lab.tests.Problem10Test
java -cp out edu.lab.tests.Problem11Test
java -cp out edu.lab.tests.Problem12Test

8) Text Analyzer (Interfaces + Strings + Packages)

Goal: Build a text analyzer using an interface; practice split, length, indexOf, contains.

Packages & files

• edu.lab.api.Analyzer
• edu.lab.text.SimpleAnalyzer (implements Analyzer)

Method signatures

package edu.lab.api;
public interface Analyzer {
    int countWords(String text);
    int countCharacters(String text);
    boolean containsSubstring(String text, String sub);
}

package edu.lab.text;
import edu.lab.api.Analyzer;
public class SimpleAnalyzer implements Analyzer {
    public SimpleAnalyzer();
    @Override public int countWords(String text);
    @Override public int countCharacters(String text);
    @Override public boolean containsSubstring(String text, String sub);
}

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9) Palindrome Utilities (StringBuffer + Packages)

Goal: Practice immutability of String, use StringBuffer.reverse();

Packages & files

• edu.lab.util.PalindromeUtil

Method signatures

package edu.lab.util;
public final class PalindromeUtil {
    private PalindromeUtil() {}
    public static boolean isPalindrome(String text); // ignore case & spaces
    public static String reverse(String text);       // use StringBuffer.reverse()
}

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10) Comparable Employee (Interfaces + String compare + Packages)

Goal: Implement ordering via Comparable<T>; sort by name case-insensitively;

Packages & files

• edu.lab.model.Employee (implements Comparable<Employee>)

Method signatures

package edu.lab.model;
public class Employee implements Comparable<Employee> {
    public Employee(int id, String name);
    public int getId();
    public String getName();
    @Override public int compareTo(Employee other); // compare by name, case-insensitive
    @Override public String toString();             // "Employee{id=.., name='..'}"
    @Override public boolean equals(Object o);      // consistent with compareTo by name
    @Override public int hashCode();
}

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11) Shape API (Interfaces + toString + Packages)

Goal: Separate API from implementations; demonstrate polymorphism through an interface and package imports.

Packages & files

• edu.lab.shapes.api.Shape
• edu.lab.shapes.impl.Circle
• edu.lab.shapes.impl.Rectangle

Method signatures

package edu.lab.shapes.api;
public interface Shape {
    double area();
    double perimeter();
}

package edu.lab.shapes.impl;
import edu.lab.shapes.api.Shape;
public class Circle implements Shape {
    public Circle(double radius);
    public double getRadius();
    @Override public double area();
    @Override public double perimeter();
    @Override public String toString(); // "Circle{r=.., area=.., perim=..}"
}

package edu.lab.shapes.impl;
import edu.lab.shapes.api.Shape;
public class Rectangle implements Shape {
    public Rectangle(double width, double height);
    public double getWidth();
    public double getHeight();
    @Override public double area();
    @Override public double perimeter();
    @Override public String toString(); // "Rectangle{w=.., h=.., area=.., perim=..}"
}

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12) String Search Strategy (Multiple Implementations + Packages)

Goal: Two interchangeable search strategies via an interface; practice case-sensitive vs. case-insensitive search and replace.

Packages & files

• edu.lab.search.Searchable
• edu.lab.search.CaseSensitiveSearch
• edu.lab.search.CaseInsensitiveSearch

Method signatures

package edu.lab.search;
public interface Searchable {
    boolean search(String text, String key);
    String replace(String text, String oldWord, String newWord);
}

package edu.lab.search;
public class CaseSensitiveSearch implements Searchable {
    public CaseSensitiveSearch();
    @Override public boolean search(String text, String key);          // use indexOf
    @Override public String replace(String text, String oldWord, String newWord);
}

package edu.lab.search;
public class CaseInsensitiveSearch implements Searchable {
    public CaseInsensitiveSearch();
    @Override public boolean search(String text, String key);          // toLowerCase both
    @Override public String replace(String text, String oldWord, String newWord); // case-insensitive replace
}

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Self‑Evaluation

• Compile and run each ProblemXTest.
• If the summary prints ✅ All tests passed!, your solution meets the spec.
• Do not change method signatures; implement the TODOs only.

Good luck!