设计模式与Android建造者模式——建军大业

Posted 2020-10-10

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什么是建造者模式

所谓建造者模式，就是将一个复杂对象的构建与它的表示分离，使得同样的构建过程可以创建不同的表示的设计模式。建造者模式在构建过程中隐藏了复杂的实现细节，可以大大降低代码耦合度。

建造者模式的实现方式

《水浒传》讲述了的故事，梁山泊是一个不断壮大的队伍

先写一个Troops：

public abstract class Troops {

    protected String leader;
    protected ArrayList<String> others = new ArrayList<>();
    protected String purpose;

    //领袖
    public void setLeader(String leader) {
        this.leader = leader;
    }

    //其他人
    public void setOthers(String... others) {
        for (String other:others){
            this.others.add(other);
        }
    }

    //宗旨
    public abstract void setPurpose();

    @Override
    public String toString() {
        return "Troops{" +
                "leader=‘" + leader + ‘\‘‘ +
                ", others=" + others.toString() +
                ", purpose=‘" + purpose + ‘\‘‘ +
                ‘}‘;
    }
}

这是梁山的Troops：

public class Liangshan extends Troops {

    protected Liangshan(){}

    @Override
    public void setPurpose() {
        purpose = "替天行道";
    }
}

再写一个Builder：

public abstract class Builder {

    public abstract void buildLeader(String leader);

    public abstract void buildOthers(String... others);

    public abstract void buildPurpose();

    public abstract Troops create();

}

这是好汉们的Builder：

public class LiangshanBuilder extends Builder {

    private Liangshan liangshan;

    @Override
    public void buildLeader(String leader) {
        liangshan.setLeader(leader);
    }

    @Override
    public void buildOthers(String... others) {
        liangshan.setOthers(others);
    }

    @Override
    public void buildPurpose() {
        liangshan.setPurpose();
    }

    @Override
    public Troops create() {
        return liangshan;
    }
}

接下来写一个Director：

public class Director {

    Builder mBuilder = null;

    public Director(Builder builder){
        this.mBuilder = builder;
    }

    public void construct(String leader,String... others){
        mBuilder.buildLeader(leader);
        mBuilder.buildOthers(others);
        mBuilder.buildPurpose();
    }

}

我们只需要如下代码便可以实现梁山好汉的大聚义：

Builder builder = new LiangshanBuilder();
Director director = new Director(builder);
director.construct("宋江","卢俊义","吴用","公孙胜");
Log.e("梁山",builder.create().toString());

在实际开发过程中，Director层常常被省略，由一个链式调用的Builder来进行对象的组装。我们这次用梁山好汉的对立面——方腊来举例，这次这么改写上文的Builder：

public class MingjiaoBuilder{
    private Mingjiao mingjiao;

    public MingjiaoBuilder(){
        mingjiao = new Mingjiao();
    }

    public MingjiaoBuilder buildLeader(String leader) {
        mingjiao.setLeader(leader);
        return this;
    }

    public MingjiaoBuilder buildOthers(String... others) {
        mingjiao.setOthers(others);
        return this;
    }

    public MingjiaoBuilder buildPurpose() {
        mingjiao.setPurpose();
        return this;
    }

    public Mingjiao create() {
        return mingjiao;
    }
}

当然，Troops是这样继承的：

public class Mingjiao extends Troops {
    @Override
    public void setPurpose() {
        this.purpose = "作乱犯上";
    }
}

然后方腊作乱犯上的过程是这样的：

MingjiaoBuilder builder = new MingjiaoBuilder()
        //虽是妄称天子位
        .buildLeader("方腊")
        //也须伪列宰臣班
        .buildOthers("石宝","邓元觉","方杰")
        .buildPurpose();
Log.e("明教",builder.create().toString());