Builder模式擁有重疊構造起器的安全性和JavaBeans模式的可讀性。的確，看起來程式碼舒服好多。當構造器引數比較多的時候推薦使用，構造器比較少的時候就不需要使用這個了。之前封裝OKhttp的時候，發現Request這個類就是使用這個模式，可以借鑑一下。

這個模式其實就是構建Builder靜態內部類，在Apple類的構造方法中初始化Apple物件。程式碼如下：

public class Apple {
    private final int a;
    private final int b;
    private final int c;
    private final
 
 int d;
    private final int e;

    public static class Builder {
        private final int a;
        private final int b;
        private int c = 0;
        private int d = 0;
        private int e = 0;

        public Builder(int a, int b) {
            this.a = a;
            this.b = b;
        }

        public
 
 Builder setC(int c) {
            this.c = c;
            return this;
        }

        public Builder setD(int d) {
            this.d = d;
            return this;
        }

        public Builder setE(int e) {
            this.e = e;
            return this;
        }

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

    private Apple(Builder builder) {
        this.a = builder.a;
        this.b = builder.b;
        this.c = builder.c;
        this.d = builder.d;
        this.e = builder.e;
    }

    public static void main(String[] args) {
        Apple apple = new Apple.Builder(1, 1).setC(12).setD(14).build();//初始化物件
    }


}

對比一下重疊構造器：

public class MyLinearLayout {
private int a;
private int b;
private int c;
private int d;
private int e;

public MyLinearLayout() {
this(0, 0);
    }

public MyLinearLayout(int a, int b) {
this(a, b, 0);
    }

public MyLinearLayout(int a, int b, int c) {
this(a, b, c, 0);
    }

public MyLinearLayout(int a, int b, int c, int d) {
this(a, b, c, d, 0);
    }

public MyLinearLayout(int a, int b, int c, int d, int e) {
this.a = a;
this.b = b;
this.c = c;
this.d = d;
this.e = e;
    }
}

有木有感覺可讀性高了好多。