设计模式之建造者模式

建造者模式，将一个复杂对象的构建与它的表示分离，使得构建过程可以以分部进行的链式调用来完成

若不用Build模式

定义一个Person类

public class Person {
    private String name;
    private int age;
    private double height;
    private double weight;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public double getHeight() {
        return height;
    }

    public void setHeight(double height) {
        this.height = height;
    }

    public double getWeight() {
        return weight;
    }

    public void setWeight(double weight) {
        this.weight = weight;
    }
}

可能会定义一个构造方法。

public Person(String name, int age, double height, double weight) {
	this.name = name;
	this.age = age;
	this.height = height;
	this.weight = weight;
}

对应不同的需求，可能会定义好几种构造方法

public Person(String name) {
	this.name = name;
}

public Person(String name, int age) {
	this.name = name;
	this.age = age;
}

public Person(String name, int age, double height) {
	this.name = name;
	this.age = age;
	this.height = height;
}

使用的时候就变成这样了

Person p1=new Person();
Person p2=new Person("张三");
Person p3=new Person("李四",18);
Person p4=new Person("王五",21,180);
Person p5=new Person("赵六",17,170,65.4);

这样的坏处：

• 构造函数有多个参数，不好确定每个参数具体意思，可读性不强
• 若参数较多的时候，麻烦

若使用Builder模式

具体代码实现

public class Person {
    private String name;
    private int age;
    private double height;
    private double weight;

    privatePerson(Builder builder) {
        this.name=builder.name;
        this.age=builder.age;
        this.height=builder.height;
        this.weight=builder.weight;
    }
    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public double getHeight() {
        return height;
    }

    public void setHeight(double height) {
        this.height = height;
    }

    public double getWeight() {
        return weight;
    }

    public void setWeight(double weight) {
        this.weight = weight;
    }

    static class Builder{
        private String name;
        private int age;
        private double height;
        private double weight;
        public Builder name(String name){
            this.name=name;
            return this;
        }
        public Builder age(int age){
            this.age=age;
            return this;
        }
        public Builder height(double height){
            this.height=height;
            return this;
        }

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

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

大概流程

• 定义静态Builder类
• Builder类中声明和外部类一样的变量
• 定义多个set方法，返回结果为Builder本身（this）
• Builder类中增加build（）方法，返回外部类Person对象
• 外部类Person中声明一个参数为Builder的构造函数

使用

Person.Builder builder=new Person.Builder();
Person person=builder
		.name("张三")
		.age(18)
		.height(178.5)
		.weight(67.4)
		.build();

Android中哪些地方使用到Builder模式

对话框的创建，AlertDialog

AlertDialog.Builder builder=new AlertDialog.Builder(this);
AlertDialog dialog=builder.setTitle("标题")
		.setIcon(android.R.drawable.ic_dialog_alert)
		.setView(R.layout.myview)
		.setPositiveButton(R.string.positive, new DialogInterface.OnClickListener() {
			@Override
			public void onClick(DialogInterface dialog, int which) {

			}
		})
		.setNegativeButton(R.string.negative, new DialogInterface.OnClickListener() {
			@Override
			public void onClick(DialogInterface dialog, int which) {

			}
		})
		.create();
dialog.show();