Java通过Builder创建实例

昨晚做测试的时候需要一个测试对象，于是创建了一个Person，如下：

public class Person implements Serializable{
    private final int age;
    private final String name;
    private int weight;
    private String sex;
    .....
}

 可见这个对象的域有多么的多，如果在构造函数中进行赋值，或者实例化后通过setter赋值，都是件十分麻烦的事，于是便想到了Effective Java中通过创建内部类Builder来构造实例：

 

public static class Builder {
	
	// 必须
	private final int age;
	private final String name;
	
	// 非必须
	private String sex = "";
	private int weight = 0;
	
	public Builder (int age, String name){
		this.age = age;
		this.name = name;
	}
	
	public Builder sex (String val){
		sex = val;
		return this;
	}
	public Builder weight (int val){
		weight = val;
		return this;
	}
	
	public Person build (){
		return new Person(this);
	}
	
}

 

这样一来就能很方便到选择需要的参数进行赋值了：

Person person = new Person.Builder(20, "张三").sex("男").weight(140).build();

 

很清晰吧，下面是完整代码：

public class Person implements Serializable{

	private static final long serialVersionUID = 7037233268790765128L;
	
	private final int age;
	private final String name;
	private final String sex;
	private final int weight;
	
	private Person (Builder builder){
		age = builder.age;
		name = builder.name;
		sex = builder.sex;
		weight = builder.weight;
	}

	public static class Builder {
		
		// 必须
		private final int age;
		private final String name;
		
		// 非必须
		private String sex = "";
		private int weight = 0;
		
		public Builder (int age, String name){
			this.age = age;
			this.name = name;
		}
		
		public Builder sex (String val){
			sex = val;
			return this;
		}
		public Builder weight (int val){
			weight = val;
			return this;
		}
		
		public Person build (){
			return new Person(this);
		}
		
	}
	

	public int getAge() {
		return age;
	}

	public String getName() {
		return name;
	}

	public String getSex() {
		return sex;
	}

	public int getWeight() {
		return weight;
	}

	@Override
	public String toString() {
		return "Person [age=" + age + ", name=" + name + ", sex=" + sex
				+ ", weight=" + weight + "]";
	}
	
}