Printing all variables value from a class
JavaReflectionJava Problem Overview
I have a class with information about a Person that looks something like this:
public class Contact {
private String name;
private String location;
private String address;
private String email;
private String phone;
private String fax;
public String toString() {
// Something here
}
// Getters and setters.
}
I want toString() to return this.name +" - "+ this.locations + ... for all variables. I was trying to implement it using reflection as shown from this question but I can't manage to print instance variables.
What is the correct way to solve this?
Java Solutions
Solution 1 - Java
From Implementing toString:
public String toString() {
StringBuilder result = new StringBuilder();
String newLine = System.getProperty("line.separator");
result.append( this.getClass().getName() );
result.append( " Object {" );
result.append(newLine);
//determine fields declared in this class only (no fields of superclass)
Field[] fields = this.getClass().getDeclaredFields();
//print field names paired with their values
for ( Field field : fields ) {
result.append(" ");
try {
result.append( field.getName() );
result.append(": ");
//requires access to private field:
result.append( field.get(this) );
} catch ( IllegalAccessException ex ) {
System.out.println(ex);
}
result.append(newLine);
}
result.append("}");
return result.toString();
}
Solution 2 - Java
Why do you want to reinvent the wheel when there are opensource that are already doing the job pretty nicely.
Both apache common-langs and spring support some very flexible builder pattern
For apache, here is how you do it reflectively
@Override
public String toString()
{
return ToStringBuilder.reflectionToString(this);
}
Here is how you do it if you only want to print fields that you care about.
@Override
public String toString()
{
return new ToStringBuilder(this)
.append("name", name)
.append("location", location)
.append("address", address)
.toString();
}
You can go as far as "styling" your print output with non-default ToStringStyle or even customizing it with your own style.
I didn't personally try spring ToStringCreator api, but it looks very similar.
Solution 3 - Java
If you are using Eclipse, this should be easy:
1.Press Alt+Shift+S
2.Choose "Generate toString()..."
Enjoy! You can have any template of toString()s.
This also works with getter/setters.
Solution 4 - Java
Generic toString() one-liner, using reflection and style customization:
import org.apache.commons.lang3.builder.ReflectionToStringBuilder;
import org.apache.commons.lang3.builder.ToStringStyle;
...
public String toString()
{
return ReflectionToStringBuilder.toString(this, ToStringStyle.SHORT_PREFIX_STYLE);
}
Solution 5 - Java
When accessing the field value, pass the instance rather than null.
Why not use code generation here? Eclipse, for example, will generate a reasoble toString implementation for you.
Solution 6 - Java
Another simple approach is to let Lombok generate the toString method for you.
For this:
- Simply add
Lombokto your project - Add the annotation
@ToStringto the definition of your class - Compile your class/project, and it is done
So for example in your case, your class would look like this:
@ToString
public class Contact {
private String name;
private String location;
private String address;
private String email;
private String phone;
private String fax;
// Getters and setters.
}
Example of output in this case:
Contact(name=John, location=USA, address=SF, email=foo@bar.com, phone=99999, fax=88888)
More details about how to use the annotation @ToString.
NB: You can also let Lombok generate the getters and setters for you, here is the full feature list.
Solution 7 - Java
If the output from ReflectionToStringBuilder.toString() is not enough readable for you, here is code that:
-
sorts field names alphabetically
-
flags non-null fields with asterisks in the beginning of the line
public static Collection
getAllFields(Class type) { TreeSet fields = new TreeSet ( new Comparator () { @Override public int compare(Field o1, Field o2) { int res = o1.getName().compareTo(o2.getName()); if (0 != res) { return res; } res = o1.getDeclaringClass().getSimpleName().compareTo(o2.getDeclaringClass().getSimpleName()); if (0 != res) { return res; } res = o1.getDeclaringClass().getName().compareTo(o2.getDeclaringClass().getName()); return res; } }); for (Class c = type; c != null; c = c.getSuperclass()) { fields.addAll(Arrays.asList(c.getDeclaredFields())); } return fields; } public static void printAllFields(Object obj) { for (Field field : getAllFields(obj.getClass())) { field.setAccessible(true); String name = field.getName(); Object value = null; try { value = field.get(obj); } catch (IllegalArgumentException | IllegalAccessException e) { e.printStackTrace(); } System.out.printf("%s %s.%s = %s;\n", value==null?" ":"*", field.getDeclaringClass().getSimpleName(), name, value); } }
test harness:
public static void main(String[] args) {
A a = new A();
a.x = 1;
B b = new B();
b.x=10;
b.y=20;
System.out.println("=======");
printAllFields(a);
System.out.println("=======");
printAllFields(b);
System.out.println("=======");
}
class A {
int x;
String z = "z";
Integer b;
}
class B extends A {
int y;
private double z = 12345.6;
public int a = 55;
}
Solution 8 - Java
Addition with @cletus answer, You have to fetch all model fields(upper hierarchy) and set field.setAccessible(true) to access private members. Here is the full snippet:
@Override
public String toString() {
StringBuilder result = new StringBuilder();
String newLine = System.getProperty("line.separator");
result.append(getClass().getSimpleName());
result.append( " {" );
result.append(newLine);
List<Field> fields = getAllModelFields(getClass());
for (Field field : fields) {
result.append(" ");
try {
result.append(field.getName());
result.append(": ");
field.setAccessible(true);
result.append(field.get(this));
} catch ( IllegalAccessException ex ) {
// System.err.println(ex);
}
result.append(newLine);
}
result.append("}");
result.append(newLine);
return result.toString();
}
private List<Field> getAllModelFields(Class aClass) {
List<Field> fields = new ArrayList<>();
do {
Collections.addAll(fields, aClass.getDeclaredFields());
aClass = aClass.getSuperclass();
} while (aClass != null);
return fields;
}
Solution 9 - Java
i will get my answer as follow:
import java.io.IOException;
import java.io.Writer;
import java.lang.reflect.Array;
import java.lang.reflect.Field;
import java.util.HashMap;
import java.util.Map;
public class findclass {
public static void main(String[] args) throws Exception, IllegalAccessException {
new findclass().findclass(new Object(), "objectName");
new findclass().findclass(1213, "int");
new findclass().findclass("ssdfs", "String");
}
public Map<String, String>map=new HashMap<String, String>();
public void findclass(Object c,String name) throws IllegalArgumentException, IllegalAccessException {
if(map.containsKey(c.getClass().getName() + "@" + Integer.toHexString(c.hashCode()))){
System.out.println(c.getClass().getSimpleName()+" "+name+" = "+map.get(c.getClass().getName() + "@" + Integer.toHexString(c.hashCode()))+" = "+c);
return;}
map.put(c.getClass().getName() + "@" + Integer.toHexString(c.hashCode()), name);
Class te=c.getClass();
if(te.equals(Integer.class)||te.equals(Double.class)||te.equals(Float.class)||te.equals(Boolean.class)||te.equals(Byte.class)||te.equals(Long.class)||te.equals(String.class)||te.equals(Character.class)){
System.out.println(c.getClass().getSimpleName()+" "+name+" = "+c);
return;
}
if(te.isArray()){
if(te==int[].class||te==char[].class||te==double[].class||te==float[].class||te==byte[].class||te==long[].class||te==boolean[].class){
boolean dotflag=true;
for (int i = 0; i < Array.getLength(c); i++) {
System.out.println(Array.get(c, i).getClass().getSimpleName()+" "+name+"["+i+"] = "+Array.get(c, i));
}
return;
}
Object[]arr=(Object[])c;
for (Object object : arr) {
if(object==null)
System.out.println(c.getClass().getSimpleName()+" "+name+" = null");
else {
findclass(object, name+"."+object.getClass().getSimpleName());
}
}
}
Field[] fields=c.getClass().getDeclaredFields();
for (Field field : fields) {
field.setAccessible(true);
if(field.get(c)==null){
System.out.println(field.getType().getSimpleName()+" "+name+"."+field.getName()+" = null");
continue;
}
findclass(field.get(c),name+"."+field.getName());
}
if(te.getSuperclass()==Number.class||te.getSuperclass()==Object.class||te.getSuperclass()==null)
return;
Field[]faFields=c.getClass().getSuperclass().getDeclaredFields();
for (Field field : faFields) {
field.setAccessible(true);
if(field.get(c)==null){
System.out.println(field.getType().getSimpleName()+" "+name+"<"+c.getClass().getSuperclass().getSimpleName()+"."+field.getName()+" = null");
continue;
}
Object check=field.get(c);
findclass(field.get(c),name+"<"+c.getClass().getSuperclass().getSimpleName()+"."+field.getName());
}
}
public void findclass(Object c,String name,Writer writer) throws IllegalArgumentException, IllegalAccessException, IOException {
if(map.containsKey(c.getClass().getName() + "@" + Integer.toHexString(c.hashCode()))){
writer.append(c.getClass().getSimpleName()+" "+name+" = "+map.get(c.getClass().getName() + "@" + Integer.toHexString(c.hashCode()))+" = "+c+"\n");
return;}
map.put(c.getClass().getName() + "@" + Integer.toHexString(c.hashCode()), name);
Class te=c.getClass();
if(te.equals(Integer.class)||te.equals(Double.class)||te.equals(Float.class)||te.equals(Boolean.class)||te.equals(Byte.class)||te.equals(Long.class)||te.equals(String.class)||te.equals(Character.class)){
writer.append(c.getClass().getSimpleName()+" "+name+" = "+c+"\n");
return;
}
if(te.isArray()){
if(te==int[].class||te==char[].class||te==double[].class||te==float[].class||te==byte[].class||te==long[].class||te==boolean[].class){
boolean dotflag=true;
for (int i = 0; i < Array.getLength(c); i++) {
writer.append(Array.get(c, i).getClass().getSimpleName()+" "+name+"["+i+"] = "+Array.get(c, i)+"\n");
}
return;
}
Object[]arr=(Object[])c;
for (Object object : arr) {
if(object==null){
writer.append(c.getClass().getSimpleName()+" "+name+" = null"+"\n");
}else {
findclass(object, name+"."+object.getClass().getSimpleName(),writer);
}
}
}
Field[] fields=c.getClass().getDeclaredFields();
for (Field field : fields) {
field.setAccessible(true);
if(field.get(c)==null){
writer.append(field.getType().getSimpleName()+" "+name+"."+field.getName()+" = null"+"\n");
continue;
}
findclass(field.get(c),name+"."+field.getName(),writer);
}
if(te.getSuperclass()==Number.class||te.getSuperclass()==Object.class||te.getSuperclass()==null)
return;
Field[]faFields=c.getClass().getSuperclass().getDeclaredFields();
for (Field field : faFields) {
field.setAccessible(true);
if(field.get(c)==null){
writer.append(field.getType().getSimpleName()+" "+name+"<"+c.getClass().getSuperclass().getSimpleName()+"."+field.getName()+" = null"+"\n");
continue;
}
Object check=field.get(c);
findclass(field.get(c),name+"<"+c.getClass().getSuperclass().getSimpleName()+"."+field.getName(),writer);
}
}
}