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優良 Java 程式碼風格指南（下）

編輯：Java 相關知識

前言

承接第一部分，本文將說明更多良好風格要素，並為本系列畫下句點。

原始碼檔案組織

一個良好的 Java 原始碼檔案建議依序包含：

檔案標頭註解（可選）
套件宣告
空行或分隔符
Import 陳述句
空行或分隔符
類別定義

範例 1：不良檔案組織

package org.rotpad;
import java.awt.*;
import javax.swing.event.*;
import org.javacogs.*;
import javax.swing.*;
import java.awt.event.*;
class Foo { ... }
public class RotPad extends JFrame { ... }

範例 2：良好檔案組織

package org.rotpad;
// Java classes
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;
// JavaCogs classes
import org.javacogs.*;

/**
 * RotPad is a simple GUI application for performing rotation ciphers on plain
 * text.
 *
 * @author Thornton Rose
 * @version 1.0
 */
public class RotPad extends JFrame { ... }

//-----------------------------------------------------------------------------
/**
 * Foo is ...
 *
 * @author Thornton Rose
 * @version 1.0
 */
class Foo { ... }

Import 陳述句組織

匯入類別眾多時，建議依下列順序分組並加註解：

Java 標準類別 (java.*)
Java 擴充類別 (javax.*)
第三方類別
專案類別

追求完美者可在各組內按字母排序。

範例 3：不良 Import 風格

import java.util.*;
import javax.swing.*;
import java.awt.event*;
import com.gensym.com.*;
import javax.swing.table.*;
import com.pv.jfcx.*;
import java.awt.*;
import com.melthorn.util.*;

範例 4a：良好 Import 風格（行尾註解）

import java.awt.*;
import java.awt.event.*;
import java.util.*;
import javax.swing.table.*;
import com.gensym.com.*; // BeanXporter
import com.pv.jfcx.*; // ProtoView
import com.melthorn.util.*; // Utilities

範例 4b：良好 Import 風格（區塊註解）

// Java classes
import java.awt.*;
import java.awt.event.*;
import java.util.*;
import javax.swing.table.*;
// BeanXporter
import com.gensym.com.*;
// ProtoView GUI components
import com.pv.jfcx.*;
// Application classes
import com.melthorn.util.*;

類別內部結構

建議順序：

Javadoc 註解
類別宣告
欄位宣告
空行分隔
建構子
空行分隔
方法（main() 除外），邏輯分組
空行分隔
內部類別
空行分隔
main() 方法

範例 5：不良類別風格

// RotPad -- GUI app. for ROT ciphering
public class RotPad extends JFrame {
    private static final String TRANSFORM_ROT13 = "ROT13";
    private static final String TRANSFORM_ROT13N5 = "ROT13N5";
    private static final String TRANSFORM_ROTASCII = "ROT-ASCII";
    private void jbInit() throws Exception { ... }
    public static final String TITLE = "RotPad";
    public static final String VERSION = "1.0";
    public static void main(String[] args) { ... }
    public RotPad() { ... }
    private JPanel jPanel1 = new JPanel();
    private JPanel jPanel2 = new JPanel();
    private BorderLayout borderLayout1 = new BorderLayout();
    ...
}

範例 6：良好類別風格

/**
 * RotPad is a simple GUI application for performing rotation ciphers on plain
 * text.
 *
 * @author Thornton Rose
 * @version 1.0
 */
public class RotPad extends JFrame {
    // Public constants
    public static final String TITLE = "RotPad";
    public static final String VERSION = "1.0";
    // Private constants
    private static final String TRANSFORM_ROT13 = "ROT13";
    private static final String TRANSFORM_ROT13N5 = "ROT13N5";
    private static final String TRANSFORM_ROTASCII = "ROT-ASCII";
    // GUI components [JBuilder generated]
    private BorderLayout borderLayout1 = new BorderLayout();
    private JPanel jPanel1 = new JPanel();
    private JPanel jPanel2 = new JPanel();
    ...

    /**
     * Construct a new instance of this class.
     */
    public RotPad() { ... }

    /**
     * Initialize UI components. [JBuilder generated]
     */
    private void jbInit() throws Exception { ... }

    ...
    //--------------------------------------------------------------------------
    /**
     * Start the application.
     */
    public static void main(String[] args) { ... }
}

欄位宣告規範

大量欄位時依存取層級與性質分組：

Public constants
Public variables
Protected constants
Protected variables
Package constants
Package variables
Private constants
Private variables

輔助準則：

每行一個宣告。
Public/Protected 欄位至少加 Javadoc 註解。
常數名稱全大寫。
IDE 產生的 GUI 欄位獨立區隔，利維護。

範例 7：不良欄位風格

public class CustomerSearchDialog extends JDialog {
    private JLabel firstNameLabel = new JLabel();
    private JLabel lastNameLabel = new JLabel();
    public static final RESULT_SELECT = 1;
    private Vector results = new Vector(); // Search results.
    private DefaultTableModel tableModel = new DefaultTableModel();
    public static final RESULT_CANCEL = 0;
    // ...
}

範例 8：良好欄位風格

/**
 * ...
 */
public class CustomerSearchDialog extends JDialog {
    /**
     * Indicates that search was cancelled; returned by showDialog() when
     * user clicks cancel button.
     */
    public static final RESULT_CANCEL = 0;
    /**
     * Indicates that a customer was selected; returned by showDialog() when
     * user clicks select button.
     */
    public static final RESULT_SELECT = 1;
    private Vector results = new Vector(); // Search results.
    private DefaultTableModel tableModel = new DefaultTableModel(); // Grid model.
    // GUI fields. [JBuilder]
    private JLabel firstNameLabel = new JLabel();
    private JLabel lastNameLabel = new JLabel();
    // ...
}

方法宣告規範

務必有 Javadoc 或標頭註解。
存取修飾字放最前。
行過長時換行。
參數過多時每行一個。
方法名與左括號間無空白。
右括號與左大括號間有空白（可換行）。

範例 9：不良方法風格

public int getTypeCount (String custType)
{
    ...
}
static public getInstance(){ ... };
public void showRange()
throws RangeException {
    ...
}

範例 10：良好方法風格


/**
 * Return the single instance of this class.
 */
public static CalculationEngine getInstance() {
    return instance;
}

/**
 * Calculate the consumption coefficient.
 */
public float calculateConsumptionCoefficient(int base, float variance,
    int iterations) throws RangeException {
    // ...
}

/**
 * Calculate the consumption coefficient.
 */
public float calculateConsumptionCoefficient(
    int base,
    float variance,
    int iterations)
    throws RangeException
{
    // ...
}