Get Fields using Reflection

In this example we shall explain with a simple example to get the fields of a class using the reflection. You can list the public and private fields of an object using the following steps:

• Get the Class instance of the class which you want to list the fields. In this example get the Class instance of Math class.
• Call getFields() method from the Class instance which returns the Field[] array which contains the public fields.
• Call getDeclaredFields() method from the Class instance which returns the Field[] array which contains all the fields whether it is private, public or default.

Lets look at this example to list of fields of java.lang.Math class:

[code lang=”java”] package javabeat.net.reflection;

import java.lang.reflect.Field;

public class JavaBeatReflectionExample {

public static void main(String[] args) throws Exception {

// Get the Class instance for Math
Class<?> mathClass = java.lang.Math.class;

//Declare Fields class
Field[] refFields;

// List all the public fields in the Math class
refFields = mathClass.getFields();
for (int i = 0; i < refFields.length; i++) {
System.out.println("Public Field: " + refFields[i]);
}

System.out.println();

// List all the fields in the Math class
refFields = mathClass.getDeclaredFields();
for (int i = 0; i < refFields.length; i++) {
System.out.println("Field: " + refFields[i]);
}

}
}
[/code]

Output

[code] Public Field: public static final double java.lang.Math.E
Public Field: public static final double java.lang.Math.PI

Field: public static final double java.lang.Math.E
Field: public static final double java.lang.Math.PI
Field: private static java.util.Random java.lang.Math.randomNumberGenerator
Field: private static long java.lang.Math.negativeZeroFloatBits
Field: private static long java.lang.Math.negativeZeroDoubleBits
[/code]