Java find class fields with specified data type
By：Roy.LiuLast updated：2019-08-17
Some Java reflection API examples.
1. Display all fields and data type
A Java reflection example to loop over all the fields declared by a class.
1.1 A POJO.
CompanyA.java
package com.mkyong.test;
import java.util.List;
import java.util.Map;
import java.util.Set;
public class CompanyA {
String orgName;
int count;
List<String> comments;
Set<String> branches;
Map<String, String> extra;
//...
1.2 Use Java reflection APIs getDeclaredFields() to loop over and display the field name and data type.
Test.java
package com.mkyong.test;
import java.lang.reflect.Field;
import java.util.List;
public class Test {
public static void main(String[] args) {
Field[] fields = CompanyA.class.getDeclaredFields();
for(Field f : fields){
Class t = f.getType();
System.out.println("field name : " + f.getName() + " , type : " + t);
Output
field name : orgName , type :class java.lang.String field name : count , type :int field name : comments , type :interface java.util.List field name : branches , type :interface java.util.Set field name : extra , type :interface java.util.Map
2. Find class fields with specified data type
2.1 This example will find all fields with List data type.
Test.java
package com.mkyong.test;
import java.lang.reflect.Field;
import java.util.ArrayList;
import java.util.List;
public class TestAbc {
public static void main(String[] args) {
List<String> list = getFieldNameWithListDataType();
for(String data : list){
System.out.println("List : " + data);
private static List<String> getFieldNameWithListDataType(){
List<String> result = new ArrayList<>();
//CompanyA, refer 1.1
Field[] fields = CompanyA.class.getDeclaredFields();
for(Field f : fields){
// use equals to compare the data type.
if(f.getType().equals(List.class)){
result.add(f.getName());
//for other data type
//Map
//if(f.getType().equals(Map.class))
//Set
//if(f.getType().equals(Set.class))
//primitive int
//if(f.getType().equals(int.class))
//if(f.getType().equals(Integer.TYPE))
//primitive long
//if(f.getType().equals(long.class))
//if(f.getType().equals(Long.TYPE))
return result;
Output
comments
Note
For primitive types like int, you can compare with int.class or Integer.TYPE
For primitive types like int, you can compare with int.class or Integer.TYPE
References
From：一号门
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