Calculate Age from Date of Birth (Java/Android SourceCode)

Here is the concept for calculating Age from a user defined or selected Date of Birth. I've used Ecplise IDE to develop an android application. But, the MainActivity.class source code can also be used in Java.

Steps in Android:

A. Create XML layout with

• DataPicker (pre-defined data object)
• Button (onClick that will handle setting values within respective text view objects)
• TextView (object to get DOB)
• TextView (object to show Age)

B. Create Package-Class called MainActivity

0. Import the necessary widgets

• import java.util.Calendar;
• import android.app.Activity;
• import android.os.Bundle;
• import android.view.Menu;
• import android.view.View;
• import android.view.View.OnClickListener;
• import android.widget.Button;
• import android.widget.DatePicker;
• import android.widget.TextView;
• import com.example.datedemo.R;

1. Initiate DataPicker, TextView elements by importing declaring and importing pre-defined respective classes

•  DatePicker picker;
• TextView tvdob;
• TextView tvage;

2. Override onCreate bundle and setContentView

• setContentView(R.layout.date);

3. Allocate Memory for initiated objects within onCreate bundle

btnsubmit=(Button)findViewById(R.id.button1);

picker =(DatePicker) findViewById(R.id.datePicker1);

tvdob=(TextView)findViewById(R.id.tvdob);

tvage=(TextView)findViewById(R.id.tvage);

4. Create OnClick event handler within onCreate bundle

btnsubmit.setOnClickListener(new OnClickListener() {

@Override
public void onClick(View view) {
// TODO Auto-generated method stub

//getDateofBirth() receives values from the custom method declared public below
tvdob.setText(getDateofBirth());

//currentDate() receives values from the custom method declared public below
tvage.setText(currentDate());

}
});

5. Create custom method to receive Date of Birth from the picker object values selected:

• public String getDateofBirth(){

  StringBuilder builder=new StringBuilder();

builder.append("DOB: ");

builder.append((picker.getMonth() + 1)+"/");//month is 0 based

builder.append(picker.getDayOfMonth()+"/");

builder.append(picker.getYear());

return builder.toString();

    }

5. Create custom method to receive Current Date Values from Calendar Object (CALENDAR WIDGET SHOULD BE IMPORTED):

• public String currentDate(){

StringBuilder todaydate=new StringBuilder();

//get today's date

Calendar today=Calendar.getInstance();

//calculate age by subtracting today's date year from the user's (picker object) selected date year 

int age=today.get(Calendar.YEAR)-picker.getYear();

if (today.get(Calendar.MONTH) < picker.getYear()) {

 age--;  

} else if (today.get(Calendar.MONTH) == picker.getYear()

   && today.get(Calendar.DAY_OF_MONTH) < picker.getYear()) {

 age--;  

}

todaydate.append("Age: ");

todaydate.append(String.valueOf(age));

return todaydate.toString();

}

C. Declare the manifest file with the the and details.

D. Run the application and sip on a cup of coffee, while you take pride in the new bit code you executed and learnt :-)

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Just in case, the lazy boy in you wants just to copy/paste the code and perform a quick fix, here following is the full source code for MainActivity.class:

//source beings here

package com.datepick; //your Gen package name

import java.util.Calendar;

import android.app.Activity;

import android.os.Bundle;

import android.view.Menu;

import android.view.View;

import android.view.View.OnClickListener;

import android.widget.Button;

import android.widget.DatePicker;

import android.widget.TextView;

import com.example.datedemo.R; //your package name

public class MainActivity extends Activity{

//Create Instance 

DatePicker picker;

TextView tvdob;

TextView tvage;

@Override

protected void onCreate(Bundle savedInstanceState) {

// TODO Auto-generated method stub

super.onCreate(savedInstanceState);

setContentView(R.layout.date);

//Allocate memory

Button btnsubmit=(Button)findViewById(R.id.button1);

picker =(DatePicker) findViewById(R.id.datePicker1);

tvdob=(TextView)findViewById(R.id.tvdob);

tvage=(TextView)findViewById(R.id.tvage);

btnsubmit.setOnClickListener(new OnClickListener() {

@Override

public void onClick(View view) {

// TODO Auto-generated method stub

tvdob.setText(getDateofBirth());

tvage.setText(currentDate());

}

});

}

public String getDateofBirth(){

  StringBuilder builder=new StringBuilder();

builder.append("DOB: ");

builder.append((picker.getMonth() + 1)+"/");//month is 0 based

builder.append(picker.getDayOfMonth()+"/");

builder.append(picker.getYear());

return builder.toString();

    }

public String currentDate(){

StringBuilder todaydate=new StringBuilder();

Calendar today=Calendar.getInstance();

int age=today.get(Calendar.YEAR)-picker.getYear();

if (today.get(Calendar.MONTH) < picker.getYear()) {

 age--;  

} else if (today.get(Calendar.MONTH) == picker.getYear()

   && today.get(Calendar.DAY_OF_MONTH) < picker.getYear()) {

 age--;  

}

todaydate.append("Age: ");

todaydate.append(String.valueOf(age));

return todaydate.toString();

}

@Override

public boolean onCreateOptionsMenu(Menu menu) {

// Inflate the menu; this adds items to the action bar if it is present.

getMenuInflater().inflate(R.menu.activity_main, menu);

return true;

}

}

//Code Ends

Make sure to create xml layout elements and Manifest file declarations before running the application.