Effective Java

2 创建和销毁对象

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• Builder模式简单示例

Builder模式是一种创建型设计模式，它允许你将对象的构建过程与表示分离，从而可以创建具有不同表示的复杂对象。以下是一个简单的Builder模式示例，以构建一个计算机为例：

首先，定义一个Computer类作为产品（Product）：

public class Computer {
    private String cpu;
    private String ram;
    private String hdd;
    private String graphicsCard;

    // Private constructor to prevent direct instantiation from outside
    private Computer(ComputerBuilder builder) {
        this.cpu = builder.cpu;
        this.ram = builder.ram;
        this.hdd = builder.hdd;
        this.graphicsCard = builder.graphicsCard;
    }

    // Getters (no setters since we want immutability)

    public String getCpu() {
        return cpu;
    }

    public String getRam() {
        return ram;
    }

    public String getHdd() {
        return hdd;
    }

    public String getGraphicsCard() {
        return graphicsCard;
    }

    // Inner static Builder class
    public static class ComputerBuilder {
        private String cpu;
        private String ram;
        private String hdd;
        private String graphicsCard;

        public ComputerBuilder() {}

        public ComputerBuilder setCpu(String cpu) {
            this.cpu = cpu;
            return this;
        }

        public ComputerBuilder setRam(String ram) {
            this.ram = ram;
            return this;
        }

        public ComputerBuilder setHdd(String hdd) {
            this.hdd = hdd;
            return this;
        }

        public ComputerBuilder setGraphicsCard(String graphicsCard) {
            this.graphicsCard = graphicsCard;
            return this;
        }

        public Computer build() {
            return new Computer(this);
        }
    }
}

接下来，你可以使用ComputerBuilder来创建Computer对象，同时利用链式调用来使代码更简洁：

public class Main {
    public static void main(String[] args) {
        Computer computer = new Computer.ComputerBuilder()
                .setCpu("Intel i7")
                .setRam("16GB DDR4")
                .setHdd("1TB SSD")
                .setGraphicsCard("NVIDIA RTX 3080")
                .build();

        System.out.println("Built Computer with specs: ");
        System.out.println("CPU: " + computer.getCpu());
        System.out.println("RAM: " + computer.getRam());
        System.out.println("HDD: " + computer.getHdd());
        System.out.println("Graphics Card: " + computer.getGraphicsCard());
    }
}

在这个例子中，ComputerBuilder负责逐步构建一个Computer实例，而实际的构建逻辑和表示（即具体的组件）是分离的。这不仅让代码更加清晰，也提供了更好的灵活性，因为你可以轻松地修改或扩展构建过程。

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