How to loop over a Class attributes in Java

Question

How can I loop over a class attributes in java dynamically   For eg    public class MyClass      private type1 att1      private type2 att2               public void function            for var in MyClass Attributes               System out println var class                       is this possible in Java

User · Answer

Accessing the fields directly is not really good style in java  I would suggest creating getter and setter methods for the fields of your bean and then using then Introspector and BeanInfo classes from the java beans package   MyBean bean   new MyBean    BeanInfo beanInfo   Introspector getBeanInfo MyBean class   for  PropertyDescriptor propertyDesc   beanInfo getPropertyDescriptors          String propertyName   propertyDesc getName        Object value   propertyDesc getReadMethod   invoke bean

User · Answer

There is no linguistic support to do what you re asking for  You can reflectively access the members of a type at run-time using reflection  e g  with Class getDeclaredFields   to get an array of Field   but depending on what you re trying to do  this may not be the best solution  See also  Java Tutorials  Reflection API   Advanced Language Topics  Reflection  Related questions  What is reflection  and why is it useful  Java Reflection  Why is it so bad  How could Reflection not lead to code smells  Dumping a java object   s properties   Example Here s a simple example to show only some of what reflection is capable of doing  import java lang reflect     public class DumpFields       public static void main String   args            inspect String class             static  lt T gt  void inspect Class lt T gt  klazz            Field   fields   klazz getDeclaredFields            System out printf  quot  d fields  n quot   fields length           for  Field field   fields                System out printf  quot  s  s  s n quot                   Modifier toString field getModifiers                     field getType   getSimpleName                    field getName                                     The above snippet uses reflection to inspect all the declared fields of class String  it produces the following output  7 fields  private final char   value private final int offset private final int count private int hash private static final long serialVersionUID private static final ObjectStreamField   serialPersistentFields public static final Comparator CASE INSENSITIVE ORDER   Effective Java 2nd Edition  Item 53  Prefer interfaces to reflection These are excerpts from the book   Given a Class object  you can obtain Constructor  Method  and Field instances representing the constructors  methods and fields of the class   They  let you manipulate their underlying counterparts reflectively  This power  however  comes at a price   You lose all the benefits of compile-time checking  The code required to perform reflective access is clumsy and verbose  Performance suffers   As a rule  objects should not be accessed reflectively in normal applications at runtime  There are a few sophisticated applications that require reflection  Examples include     omitted on purpose     If you have any doubts as to whether your application falls into one of these categories  it probably doesn t

User · Answer

Java has Reflection  java reflection     but I would suggest looking into a library like Apache Beanutils  it will make the process much less hairy than using reflection directly

User · Answer

While I agree with J  rn s answer if your class conforms to the JavaBeabs spec  here is a good alternative if it doesn t and you use Spring   Spring has a class named ReflectionUtils that offers some very powerful functionality  including doWithFields class  callback   a visitor-style method that lets you iterate over a classes fields using a callback object like this   public void analyze Object obj       ReflectionUtils doWithFields obj getClass    field - gt             System out println  Field name      field getName             field setAccessible true           System out println  Field value     field get obj                 But here s a warning  the class is labeled as  for internal use only   which is a pity if you ask me

User · Answer

Simple way to iterate over class fields and obtain values from object    Class lt   gt  c   obj getClass     Field   fields   c getDeclaredFields     Map lt String  Object gt  temp   new HashMap lt String  Object gt       for  Field field   fields          try              temp put field getName   toString    field get obj            catch  IllegalArgumentException e1            catch  IllegalAccessException e1

User · Answer

Here is a solution which sorts the properties alphabetically and prints them all together with their values   public void logProperties   throws IllegalArgumentException  IllegalAccessException     Class lt   gt  aClass   this getClass      Field   declaredFields   aClass getDeclaredFields      Map lt String  String gt  logEntries   new HashMap lt  gt        for  Field field   declaredFields        field setAccessible true        Object   arguments   new Object          field getName          field getType   getSimpleName          String valueOf field get this               String template    - Property   0   Type   1   Value   2         String logMessage   System getProperty  line separator                 MessageFormat format template  arguments        logEntries put field getName    logMessage          SortedSet lt String gt  sortedLog   new TreeSet lt  gt  logEntries keySet        StringBuilder sb   new StringBuilder  Class properties        Iterator lt String gt  it   sortedLog iterator      while  it hasNext          String key   it next        sb append logEntries get key           System out println sb toString

[java] How to loop over a Class attributes in Java?

Examples related to java

Examples related to attributes

Examples related to loops