Java中静态方法返回实例的内存管理与生命周期解析

public class MyObject {
    private int value;

    private MyObject(int value) {
        this.value = value;
    }

    // 静态工厂方法
    public static MyObject createInstance(int val) {
        return new MyObject(val); // 每次调用都会创建一个新的MyObject实例
    }

    public int getValue() {
        return value;
    }

    public static void main(String[] args) {
        MyObject obj1 = MyObject.createInstance(10);
        MyObject obj2 = MyObject.createInstance(20);

        System.out.println("Obj1 value: " + obj1.getValue());
        System.out.println("Obj2 value: " + obj2.getValue());
        // obj1 和 obj2 是两个独立的堆对象
    }
}

import java.util.ArrayList;
import java.util.List;
import java.util.Random;
import java.util.stream.Collectors;

public class RandomSumBuilder {
    private List<Integer> aList = new ArrayList<>();

    private RandomSumBuilder() { } // 构造器私有化，鼓励使用静态工厂方法

    // 静态工厂方法，每次调用都会创建并返回一个新的RandomSumBuilder实例
    public static RandomSumBuilder add() {
        RandomSumBuilder randomSumBuilder = new RandomSumBuilder();
        randomSumBuilder.aList.add(new Random().nextInt(11));
        return randomSumBuilder;
    }

    public int build() {
        return aList.stream()
                .reduce(Integer::sum)
                .orElse(0);
    }

    public static void main(String[] args) {
        for (int i = 0; i < 5; i++) {
            // 每次循环都会创建一个新的RandomSumBuilder实例
            // 该实例在表达式执行完毕后，如果没有被其他变量引用，将立即变为不可达
            System.out.println("Random sum : " + RandomSumBuilder.add().build());
        }
    }
}

public class Product {
    private final String name;
    private final double price;
    private final String description;

    private Product(Builder builder) {
        this.name = builder.name;
        this.price = builder.price;
        this.description = builder.description;
    }

    // 静态内部类作为Builder
    public static class Builder {
        private String name;
        private double price = 0.0; // 默认值
        private String description = "No description";

        public Builder name(String name) {
            this.name = name;
            return this;
        }

        public Builder price(double price) {
            this.price = price;
            return this;
        }

        public Builder description(String description) {
            this.description = description;
            return this;
        }

        public Product build() {
            return new Product(this); // 每次调用都会创建一个新的Product实例
        }
    }

    // Getter methods...
    public String getName() { return name; }
    public double getPrice() { return price; }
    public String getDescription() { return description; }

    public static void main(String[] args) {
        Product p1 = new Product.Builder()
                            .name("Laptop")
                            .price(1200.00)
                            .description("High performance laptop")
                            .build();

        Product p2 = new Product.Builder()
                            .name("Mouse")
                            .build(); // 使用默认描述和价格

        System.out.println("Product 1: " + p1.getName() + ", " + p1.getPrice());
        System.out.println("Product 2: " + p2.getName() + ", " + p2.getPrice());
    }
}