Java中多参数对象构建的优化之道：深入理解与应用构建器模式

public class ImmutableWidget {

    private final String required;
    private final String optional; // 可选属性

    // 私有构造函数，只接受Builder实例作为参数
    private ImmutableWidget(Builder builder) {
        this.required = builder.required;
        this.optional = builder.optional;
    }

    @Override
    public String toString() {
        return "Required: " + required + "; Optional: " + optional;
    }

    public String getRequired() {
        return required;
    }

    public String getOptional() {
        return optional;
    }

    // 静态嵌套的Builder类
    public static class Builder {

        private final String required; // 必需属性，在Builder构造时提供
        private String optional;       // 可选属性，通过setter方法设置

        // Builder的构造函数，用于设置必需参数
        public Builder(String required) {
            this.required = required;
        }

        // 设置可选属性的方法，返回Builder自身，支持链式调用
        public Builder setOptional(String optional) {
            this.optional = optional;
            return this; // 返回当前Builder实例
        }

        // 构建并返回ImmutableWidget实例
        public ImmutableWidget build() {
            // 可以在此处添加参数校验逻辑
            return new ImmutableWidget(this);
        }
    }

    // 示例用法
    public static void main(String... strings) {
        // 1. 只构建必需参数的对象
        ImmutableWidget widget1 = new ImmutableWidget.Builder("必需参数值A").build();
        System.out.println(widget1); // Output: Required: 必需参数值A; Optional: null

        // 2. 构建包含必需参数和可选参数的对象，使用链式调用
        ImmutableWidget widget2 = new ImmutableWidget.Builder("必需参数值B")
                                                    .setOptional("可选参数值X")
                                                    .build();
        System.out.println(widget2); // Output: Required: 必需参数值B; Optional: 可选参数值X

        // 3. 也可以分步设置
        ImmutableWidget.Builder builder = new ImmutableWidget.Builder("必需参数值C");
        // ... 可以在这里进行一些条件判断或复杂逻辑 ...
        builder.setOptional("可选参数值Y");
        ImmutableWidget widget3 = builder.build();
        System.out.println(widget3); // Output: Required: 必需参数值C; Optional: 可选参数值Y
    }
}