文章作者 ：涛姐涛哥

原文链接：

www.cnblogs.com/taojietaoge/p/11575376.html

<select id="queryBookInfo" parameterType="com.tjt.platform.entity.BookInfo" resultType="java.lang.Integer"> select count(*) from t_rule_BookInfo t where 1=1<if test="title !=null and title !='' "> AND title = #{title} </if> <if test="author !=null and author !='' "> AND author = #{author}</if> </select>

<select id="queryBookInfo" parameterType="com.tjt.platform.entity.BookInfo" resultType="java.lang.Integer"> select count(*) from t_rule_BookInfo t<where><if test="title !=null and title !='' "> title = #{title} </if><if test="author !=null and author !='' ">  AND author = #{author}</if></where> </select>

//Map 获取value 反例:HashMap<String, String> map = new HashMap<>();for (String key : map.keySet()){String value = map.get(key);}

  //Map 获取key & value 正例:HashMap<String, String> map = new HashMap<>(); for (Map.Entry<String,String> entry : map.entrySet()){     String key = entry.getKey();     String value = entry.getValue();}

LinkedList<Object> collection = new LinkedList<>();if (collection.size() == 0){  System.out.println("collection is empty."); }

LinkedList<Object> collection = new LinkedList<>();  if (collection.isEmpty()){      System.out.println("collection is empty.");  }    //检测是否为null 可以使用CollectionUtils.isEmpty()  if (CollectionUtils.isEmpty(collection)){      System.out.println("collection is null.");
  }

//初始化list，往list 中添加元素正例：  int[] arr = new int[]{1,2,3,4};  //指定集合list 的容量大小  List<Integer> list = new ArrayList<>(arr.length);  for (int i : arr){      list.add(i);  }

//在循环中拼接字符串正例 String str1 = "Love"; String str2 = "Courage"; String strConcat = str1 + str2;  //Java 编译器会对该普通模式的字符串拼接进行优化  StringBuilder sb = new StringBuilder();  for (int i = 0; i < 10; i++){     //在循环中，Java 编译器无法进行优化，所以要手动使用StringBuilder      sb.append(i);  }

//频繁调用Collection.contains() 正例  List<Object> list = new ArrayList<>();  Set<Object> set = new HashSet<>();  for (int i = 0; i <= Integer.MAX_VALUE; i++){      //时间复杂度为O(1)      if (set.contains(i)){          System.out.println("list contains "+ i);      }  }

//赋值静态成员变量反例    private static Map<String, Integer> map = new HashMap<String, Integer>(){        {            map.put("Leo",1);            map.put("Family-loving",2);            map.put("Cold on the out side passionate on the inside",3);        }    };    private static List<String> list = new ArrayList<>(){        {            list.add("Sagittarius");            list.add("Charming");            list.add("Perfectionist");        }    };

//赋值静态成员变量正例private static Map<String, Integer> map = new HashMap<String, Integer>();    static {        map.put("Leo",1);        map.put("Family-loving",2);        map.put("Cold on the out side passionate on the inside",3);    }    private static List<String> list = new ArrayList<>();    static {        list.add("Sagittarius");        list.add("Charming");        list.add("Perfectionist");    }

public class PasswordUtils {  //工具类构造函数反例  private static final Logger LOG = LoggerFactory.getLogger(PasswordUtils.class);
  public static final String DEFAULT_CRYPT_ALGO = "PBEWithMD5AndDES";
  public static String encryptPassword(String aPassword) throws IOException {      return new PasswordUtils(aPassword).encrypt();  }

public class PasswordUtils {  //工具类构造函数正例  private static final Logger LOG = LoggerFactory.getLogger(PasswordUtils.class);  //定义私有构造函数来屏蔽这个隐式公有构造函数  private PasswordUtils(){}    public static final String DEFAULT_CRYPT_ALGO = "PBEWithMD5AndDES";  public static String encryptPassword(String aPassword) throws IOException {      return new PasswordUtils(aPassword).encrypt();  }

//多余异常反例private static String fileReader(String fileName)throws IOException{
    try (BufferedReader reader = new BufferedReader(new FileReader(fileName))) {        String line;        StringBuilder builder = new StringBuilder();        while ((line = reader.readLine()) != null) {            builder.append(line);        }        return builder.toString();    } catch (Exception e) {        //仅仅是重复抛异常 未作任何处理        throw e;    }}

//多余异常正例private static String fileReader(String fileName)throws IOException{
    try (BufferedReader reader = new BufferedReader(new FileReader(fileName))) {        String line;        StringBuilder builder = new StringBuilder();        while ((line = reader.readLine()) != null) {            builder.append(line);        }        return builder.toString();        //删除多余的抛异常，或增加其他处理：        /*catch (Exception e) {            return "fileReader exception";        }*/    }}

// BigDecimal 正例BigDecimal bigDecimal1 = bigDecimal.valueOf(0.11D);

//返回null 反例public static Result[] getResults() {    return null;}
public static List<Result> getResultList() {    return null;}
public static Map<String, Result> getResultMap() {    return null;}

//返回空数组和空集正例public static Result[] getResults() {    return new Result[0];}
public static List<Result> getResultList() {    return Collections.emptyList();}
public static Map<String, Result> getResultMap() {    return Collections.emptyMap();}

//调用 equals 方法正例private static boolean fileReader(String fileName)throws IOException{
    // 使用常量或确定有值的对象来调用 equals 方法    return "Charming".equals(fileName);        //或使用：java.util.Objects.equals() 方法   return Objects.equals("Charming",fileName); }

public enum SwitchStatus {    // 枚举的属性字段反例    DISABLED(0, "禁用"),    ENABLED(1, "启用");
    public int value;    private String description;
    private SwitchStatus(int value, String description) {        this.value = value;        this.description = description;    }
    public String getDescription() {        return description;    }
    public void setDescription(String description) {        this.description = description;    }}

public enum SwitchStatus {    // 枚举的属性字段正例    DISABLED(0, "禁用"),    ENABLED(1, "启用");
    // final 修饰    private final int value;    private final String description;
    private SwitchStatus(int value, String description) {        this.value = value;        this.description = description;    }
    // 没有Setter 方法    public int getValue() {        return value;    }
    public String getDescription() {        return description;    }}

// String.split(String regex) 正例// . 需要转译String[] split2 = "a.ab.abc".split("\\.");System.out.println(Arrays.toString(split2));  // 结果为["a", "ab", "abc"]
// | 需要转译String[] split3 = "a|ab|abc".split("\\|");System.out.println(Arrays.toString(split3));  // 结果为["a", "ab", "abc"]