Android Studio是基於優秀的ide的，ide提供了豐富的功能，很方便的對程式碼進行重構，下圖是我的Android Studio Refactor選單，部分快捷鍵與預設快捷鍵不同是因為方便而修改的。

如何使用

滑鼠游標選中或者放在程式碼上，按下快捷鍵就可以彈出當前程式碼可以使用的功能。 
如下所示：

• ChangeSignature，改變函式簽名，可以修改函式的名字，引數的順序，引數的名字。

Before:

   // 改變簽名
    void testChangeSignature(int second, int first) {
        System.out.println(first + "->" + second);
    }
 

After:

    // 改變簽名
    void testChangeSignature(int one, int two) {
        System.out.println(one + "->" + two);
    }

修改前引數依次是second、first，修改是one、two。

• 修改匿名類為內部類

Before：

    // 匿名類改成內部類
    void testConvertAnonymousToInner() {
        View.OnClickListener clickListener = new View.OnClickListener() {

            @Override
            public
 
 void onClick(View v) {
                System.out.println("onClick");
            }
        };
    }

Gif:

After:

    // 匿名類改成內部類
    void testConvertAnonymousToInner() {

        View.OnClickListener clickListener = new Abc123();
    }

    private static class Abc123 implements View.OnClickListener {

        @Override
 

        public void onClick(View v) {
            System.out.println("onClick");
        }
    }

• Copy，複製一個類

Before:

    // 複製一個類
    void testCopy() {
        new FirstClass();
    }

public class FirstClass implements Serializable {

    public String first;

    @Override
    public String toString() {
        return "FirstClass{" +
                "first='" + first + '\'' +
                '}';
    }
}

Gif:

After:

public class SecondClass implements Serializable {

    public String first;

    @Override
    public String toString() {
        return "SecondClass{" +
                "first='" + first + '\'' +
                '}';
    }
}

• InvertBoolean，重構Boolean

Before:

    // 重構Boolean
    void testInvertBoolean() {
        System.out.println(checkPaswd(null));
        System.out.println(checkPaswd(""));
        System.out.println(checkPaswd("admin"));
    }

    boolean checkPaswd(String passwd) {
        if (passwd != null && passwd.length() != 0) {
            return true;
        }
        return false;
    }

Gif:

After:

    // 重構Boolean
    void testInvertBoolean() {
        System.out.println(checkPaswd(null));
        System.out.println(checkPaswd(""));
        System.out.println(checkPaswd("admin"));
    }

    boolean checkPaswd(String passwd) {
        return passwd != null && passwd.length() != 0;
    }

• ReplaceConstructorWithBuilder，構造方法變成builder

還在羨慕Picasso，Fresco人性化呼叫方式嗎？很簡單，通過這個功能就可以快速生成程式碼

Before:

public class MyAlertDialog {

    private String title;
    private String message;
    private String okButton;
    private String cancelButton;

    public MyAlertDialog(String title, String message, String okButton, String cancelButton) {
        this.title = title;
        this.message = message;
        this.okButton = okButton;
        this.cancelButton = cancelButton;
    }
}    
    // 構造方法變成builder
    void testReplaceConstructorWithBuilder() {
        new MyAlertDialog("title", "message", "ok", "cancel").show();
    }

Gif:

After:

    // 構造方法變成builder
    void testReplaceConstructorWithBuilder() {
        new MyAlertDialog.Builder()
                .setTitle("title")
                .setMessage("message")
                .setOkButton("ok")
                .setCancelButton("cancel")
                .createMyAlertDialog()
                .show();
    }

public static class Builder {
    private String title;
    private String message;
    private String okButton;
    private String cancelButton;

    public Builder setTitle(String title) {
        this.title = title;
        return this;
    }

    public Builder setMessage(String message) {
        this.message = message;
        return this;
    }

    public Builder setOkButton(String okButton) {
        this.okButton = okButton;
        return this;
    }

    public Builder setCancelButton(String cancelButton) {
        this.cancelButton = cancelButton;
        return this;
    }

    public MyAlertDialog createMyAlertDialog() {
        return new MyAlertDialog(title, message, okButton, cancelButton);
    }
}

• ReplaceConstructorWithFactory，構造方法變成工程方法

Before:

    // 構造方法變成工程方法
    void testReplaceConstructorWithFactory() {
        new MyAlertDialog("title", "message", "ok", "cancel").show();
    }

• 1
• 2
• 3
• 4

Gif:

After:

    // 構造方法變成工程方法
    void testReplaceConstructorWithFactory() {
        MyAlertDialog.newInstance("title", "message", "ok", "cancel")
                .show();
    }
public class MyAlertDialog {    
    private MyAlertDialog(String title, String message, String okButton, String cancelButton) {
        this.title = title;
        this.message = message;
        this.okButton = okButton;
        this.cancelButton = cancelButton;
    }

    public static MyAlertDialog newInstance(String title, String message, String okButton, String cancelButton) {
        return new MyAlertDialog(title, message, okButton, cancelButton);
    }
}    

通過上面程式碼發現，如果構造方法變成了工廠方式，那麼它的構造引數是private的，這樣呼叫者只能通過工廠方式來生成物件。

程式碼抽取

• ExtractParameterObject，抽取若干引數成一個類

這個比較使用，有時候一個方法引數太多，可以把這些引數合併成一個類。

Before:

    // 抽取若干引數成一個類
    void testExtractParameterObject() {
        print(100, 200);
    }

    // widht,height --> Size Class
    void print(int width, int height) {
        System.out.println("width = " + width + ", height = " + height);
    }

Gif:

After:

    // 抽取若干引數成一個類
    void testExtractParameterObject() {
        print(new Size(100, 200));
    }

    // widht,height --> Size Class
    void print(Size size) {
        System.out.println("width = " + size.getWidth() + ", height = " + size.getHeight());
    }


public class Size {
    private final int width;
    private final int height;

    public Size(int width, int height) {
        this.width = width;
        this.height = height;
    }

    public int getWidth() {
        return width;
    }

    public int getHeight() {
        return height;
    }
}    

• ExtractSuperclass，抽取到父類

Before:

    // 抽取到父類
    void testExtractSuperclass() {
        sendEvent("login_success");
    }

    public void sendEvent(Object event) {
        // EventBus.getDefault().send(event);
    }

Gif:

After:

public class BaseExtractDemo {
    public void sendEvent(Object event) {
        // EventBus.getDefault().send(event);
    }
}

public class ExtractDemo extends BaseExtractDemo {
    // 抽取到父類
    void testExtractSuperclass() {
        sendEvent("login_success");
    }
}

綜合示例

通過一個示例演示怎麼樣重構程式碼，示例是一個Activity裡面有個RecyclerView，然後重構程式碼，演示怎麼樣分離Adapter,ViewHolder等。

Before:

public class StartActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_start);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        RecyclerView recyclerView = (RecyclerView) findViewById(R.id.recyclerView);
        recyclerView.setLayoutManager(new LinearLayoutManager(this));

        final List<String> data = new ArrayList<>();
        for (int i = 0; i < 100; i++) {
            data.add("Text " + (i + 1));
        }

        recyclerView.setAdapter(new RecyclerView.Adapter<MyViewHolder>() {

            @Override
            public MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
                LayoutInflater layoutInflater = (LayoutInflater) parent.getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
                return new MyViewHolder(layoutInflater.inflate(android.R.layout.simple_list_item_1, parent, false));
            }

            @Override
            public void onBindViewHolder(MyViewHolder holder, int position) {
                holder.bind(data.get(position));
            }

            @Override
            public int getItemCount() {
                return data.size();
            }
        });
    }

    class MyViewHolder extends RecyclerView.ViewHolder {

        TextView textView;

        public MyViewHolder(View itemView) {
            super(itemView);
            textView = (TextView) itemView.findViewById(android.R.id.text1);
        }

        void bind(String text) {
            textView.setText(text);
        }
    }
}

Gif: 

After:

public class StartActivity extends AppCompatActivity {

    private RecyclerView recyclerView;
    private List<String> data;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_start);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        initData();
        initView();
    }

    private void initData() {
        data = new ArrayList<>();
        for (int i = 0; i < 100; i++) {
            data.add("Text " + (i + 1));
        }
    }

    private void initView() {
        recyclerView = (RecyclerView) findViewById(R.id.recyclerView);
        recyclerView.setLayoutManager(new LinearLayoutManager(this));
        recyclerView.setAdapter(new MyViewHolderAdapter(data));
    }
}

class MyViewHolderAdapter extends RecyclerView.Adapter<MyViewHolder> {

    private List<String> data;

    public MyViewHolderAdapter(List<String> data) {
        this.data = data;
    }

    @Override
    public MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        return MyViewHolder.newInstance(parent);
    }

    @Override
    public void onBindViewHolder(MyViewHolder holder, int position) {
        holder.bind(data.get(position));
    }

    @Override
    public int getItemCount() {
        return data.size();
    }
}


class MyViewHolder extends RecyclerView.ViewHolder {

    public static final int LAYOUT_ID = android.R.layout.simple_list_item_1;

    @NonNull
    static MyViewHolder newInstance(ViewGroup parent) {
        Context context = parent.getContext();
        LayoutInflater layoutInflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        return new MyViewHolder(layoutInflater.inflate(LAYOUT_ID, parent, false));
    }

    TextView textView;

    public MyViewHolder(View itemView) {
        super(itemView);
        textView = (TextView) itemView.findViewById(android.R.id.text1);
    }

    void bind(String text) {
        textView.setText(text);
    }
}