自定义动态添加字段内容的库类

来源：互联网发布：java nio列子编辑：程序博客网时间：2024/06/06 19:37

Java不少类可以通过Set方法动态向对象添加新的字段内容，这里面如何实现这功能且代码质量较高呢？这里我参照thinking in java的书籍，自定义一个可以在运行时动态的添加字段内容。

//自定义异常class DynamicFieldsException extends Exception {}public class DynamicFields{private Object[][] fields;//初始化保存字段内容的数组public  DynamicFields(int initialSize){fields=new Object[initialSize][2];for(int i=0;i<fields.length;i++){fields[i]=new Object[]{null,null};}}//输出内容@Overridepublic String toString(){StringBuilder result=new StringBuilder();for(Object[] filed:fields){result.append(filed[0]);result.append(":");result.append(filed[1]);result.append("\n");}return result .toString();}//查询该字段内容是否已存在private int hasField(String id){for(int i=0;i<fields.length;i++){if(id.equals(fields[i][0]))return i;}return -1;}private int getFieldNumber(String id) throws NoSuchFieldException{int fieldNum=hasField(id);if(fieldNum==-1)throw new NoSuchFieldException();return fieldNum;}private int makeField(String id){for(int i=0;i<fields.length;i++){if(fields[i][0]==null){fields[i][0]=id;return i;}}//如果数组内存已满，则重新开辟一个内存更大的数组,这里我只加一个字段内存Object[][] objects=new Object[fields.length+1][2];//拷贝字段内容for(int i=0;i<fields.length;i++){objects[i]=fields[i];}for(int i=fields.length;i<objects.length;i++){objects[i]=new Object[]{null,null};}//赋给新开辟数组内存的引用地址fields=objects;return makeField(id);}public Object getField(String id)throws NoSuchFieldException{return fields[getFieldNumber(id)][1];}public Object setField(String id,Object value)throws DynamicFieldsException{if(value==null){DynamicFieldsException fieldsException=new DynamicFieldsException();//保留最原始异常信息fieldsException.initCause(new NullPointerException());throw fieldsException;}int fieldNumber=hasField(id);if(fieldNumber==-1){fieldNumber=makeField(id);}Object result=null;try{//获取原来的字段内容result=getField(id);} catch (NoSuchFieldException e){//保留原来异常信息throw new RuntimeException(e);}//更新字段内容fields[fieldNumber][1]=value;return result;} public static void main(String[] args)  {  DynamicFields df = new DynamicFields(3);  System.out.println(df);  try   {    df.setField("d", "A value for d");    df.setField("number", 47);    df.setField("number2", 48);    System.out.println(df);    df.setField("d", "A new value for d");    df.setField("number3", 11);    System.out.println("df: " + df);    System.out.println("df.getField(\"d\") : " + df.getField("d"));    //这里将会抛出异常    Object field = df.setField("d", null);   } catch(NoSuchFieldException e)   {    e.printStackTrace(System.out);  } catch(DynamicFieldsException e)   {    e.printStackTrace(System.out);  }}}

运行结果：

null:null
null:null
null:null

d:A value for d
number:47
number2:48

df: d:A new value for d
number:47
number2:48
number3:11

df.getField("d") : A new value for d
beyondboy.DynamicFieldsException
   at beyondboy.DynamicFields.setField(DynamicFields.java:80)
   at beyondboy.DynamicFields.main(DynamicFields.java:119)
Caused by: java.lang.NullPointerException
   at beyondboy.DynamicFields.setField(DynamicFields.java:82)
   ... 1 more

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