a lot of basic java methods condensed into a few files with simplicity!

constructs_1.java

import java.util.*;

interface MyInterface {
    void doSomething();
}

enum MyEnum {
    FIRST,
    SECOND,
    THIRD
}

abstract class AbstractClass {
    abstract void doSomethingElse();
}

class ParentClass {
    void commonMethod() {
        System.out.println("Parent class method");
    }
}

class ChildClass extends ParentClass implements MyInterface {
    @Override
    public void doSomething() {
        System.out.println("Implemented method from interface");
    }

    @Override
    public void commonMethod() {
        System.out.println("Overridden method from parent class");
    }
}

class AnotherClass extends AbstractClass {
    @Override
    void doSomethingElse() {
        System.out.println("Implemented abstract method");
    }
}

public class Main {
    public static void main(String[] args) {
        ChildClass childClass = new ChildClass();
        childClass.doSomething();
        childClass.commonMethod();

        AnotherClass anotherClass = new AnotherClass();
        anotherClass.doSomethingElse();

        MyEnum first = MyEnum.FIRST;
        switch (first) {
            case FIRST:
                System.out.println("First enum value");
                break;
            case SECOND:
                System.out.println("Second enum value");
                break;
            case THIRD:
                System.out.println("Third enum value");
                break;
        }
    }
}

methods_1.java

import java.util.*;
import java.io.*;
import java.nio.file.*;

public class Example {
    public static void main(String[] args) {
        // String methods
        String str = "Hello, World!";
        System.out.println(str.substring(0, 5));
        System.out.println(str.toLowerCase());
        System.out.println(str.charAt(7));

        // File and I/O methods
        try {
            File file = new File("example.txt");
            if (!file.exists()) {
                file.createNewFile();
            }
            
            FileWriter writer = new FileWriter(file);
            writer.write(str);
            writer.close();

            String content = new String(Files.readAllBytes(Paths.get("example.txt")));
            System.out.println(content);
        } catch (IOException e) {
            e.printStackTrace();
        }

        // List and Collections methods
        List<String> list = new ArrayList<>();
        list.add("Java");
        list.add("Python");
        list.add("C++");
        System.out.println(list.get(1));

        Collections.sort(list);
        for (String language : list) {
            System.out.println(language);
        }

        // Date methods
        Date date = new Date();
        System.out.println(date.toString());

        // Math methods
        System.out.println(Math.sqrt(16));
        System.out.println(Math.max(10, 20));
    }
}