如何快速掌握Java功能开发的要点

public class SumCalculator {
    public static void main(String[] args) {
        int num1 = 10;
        int num2 = 20;
        int sum = num1 + num2;
        System.out.println("两个数的和为：" + sum);
    }
}

public class Person {
    private String name;
    private int age;
    
    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }
    
    public void sayHello() {
        System.out.println("Hello, my name is " + this.name + ". I'm " + this.age + " years old.");
    }
    
    public static void main(String[] args) {
        Person person = new Person("John", 25);
        person.sayHello();
    }
}

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

public class ListExample {
    public static void main(String[] args) {
        List<String> fruits = new ArrayList<>();
        fruits.add("apple");
        fruits.add("banana");
        fruits.add("orange");
        
        System.out.println("水果列表：");
        for (String fruit : fruits) {
            System.out.println(fruit);
        }
    }
}

public class DebugExample {
    public static void main(String[] args) {
        int n = 5;
        
        for (int i = 0; i < n; i++) {
            System.out.println("i = " + i);
        }
    }
}