它有啥用

它用于解決，通過變化無常的方式，來組織相對不變的構成要素，形成一個整體對象的問題。再強調一遍，變化的是方式，不變的是構成要素。
這種模式就是把方式和構成要素分開處理了。
其中指揮員負責不同的組裝方式。
其實這就好比木炭和金剛石都是碳元素的單質，只是因為分子結構不同結果形成了不同的物質一樣。

類圖

建造者模式.png

效果

組件0由SomeBuilder制造
組件1由SomeBuilder制造
組件2由SomeBuilder制造
生產產品
組件2由SomeBuilder制造
組件1由SomeBuilder制造
組件0由SomeBuilder制造
生產產品

Process finished with exit code 0

使用

package com.company;

public class Main {

    public static void main(String[] args) {
    // write your code here
        Director0 director0 = new Director0();
        director0.firstKindOfProduct(new SomeBuilder());

        Director1 director1 = new Director1();
        director1.secondKindOfProduct(new SomeBuilder());
    }
}

通用建造者

package com.company;

public interface CommonBuilder {
    void makeComponent0();
    void makeComponent1();
    void makeComponent2();
    Product gainProduct();
}

產品

package com.company;

public class Product {
    private String component0;
    private String component1;
    private String component2;

    public String getComponent0() {
        return component0;
    }

    public void setComponent0(String component0) {
        this.component0 = component0;
    }

    public String getComponent1() {
        return component1;
    }

    public void setComponent1(String component1) {
        this.component1 = component1;
    }

    public String getComponent2() {
        return component2;
    }

    public void setComponent2(String component2) {
        this.component2 = component2;
    }
}

某個具體的建造者

package com.company;

public class SomeBuilder implements CommonBuilder {
    private Product product;

    public SomeBuilder() {
        this.product = new Product();
    }

    @Override
    public void makeComponent0() {
        this.product.setComponent0("組件0由SomeBuilder制造");
        System.out.println(this.product.getComponent0());
    }

    @Override
    public void makeComponent1() {
        this.product.setComponent1("組件1由SomeBuilder制造");
        System.out.println(this.product.getComponent1());
    }

    @Override
    public void makeComponent2() {
        this.product.setComponent2("組件2由SomeBuilder制造");
        System.out.println(this.product.getComponent2());
    }

    @Override
    public Product gainProduct() {
        System.out.println("生產產品");
        return this.product;
    }
}

指揮者

package com.company;

public class Director0 {
    public Product firstKindOfProduct(CommonBuilder builder) {
        builder.makeComponent0();
        builder.makeComponent1();
        builder.makeComponent2();
        return builder.gainProduct();
    }
}

另一個指揮者

package com.company;

public class Director1 {
    public Product secondKindOfProduct(CommonBuilder builder) {
        builder.makeComponent2();
        builder.makeComponent1();
        builder.makeComponent0();
        return builder.gainProduct();
    }
}