How can i set up screen lock with a password programmatically?

Use this code in your App, it works for me:

DevicePolicyManager devicePolicyManager =   
             (DevicePolicyManager) getSystemService(Context.DEVICE_POLICY_SERVICE);
ComponentName demoDeviceAdmin = new ComponentName(this, name of activity);

devicePolicyManager.setPasswordQuality(
             demoDeviceAdmin,DevicePolicyManager.PASSWORD_QUALITY_UNSPECIFIED);
devicePolicyManager.setPasswordMinimumLength(demoDeviceAdmin, 5);

boolean result = devicePolicyManager.resetPassword("123456",
             DevicePolicyManager.RESET_PASSWORD_REQUIRE_ENTRY);

Toast.makeText(this, "button_lock_password_device..."+result, Toast.LENGTH_LONG).show();

Check this . This worked for me.

LockScreenActivity.java

   package com.kns;
import android.app.Activity;
import android.app.ActivityManager;
import android.app.admin.DevicePolicyManager;
import android.content.ComponentName;
import android.content.Context;
import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;

public class LockScreenActivity extends Activity implements OnClickListener {
 private Button lock;
 private Button disable;
 private Button enable;
 static final int RESULT_ENABLE = 1;

     DevicePolicyManager deviceManger;
     ActivityManager activityManager;
     ComponentName compName;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        deviceManger = (DevicePolicyManager)getSystemService(
          Context.DEVICE_POLICY_SERVICE);
        activityManager = (ActivityManager)getSystemService(
          Context.ACTIVITY_SERVICE);
        compName = new ComponentName(this, MyAdmin.class);

        setContentView(R.layout.main);

        lock =(Button)findViewById(R.id.lock);
        lock.setOnClickListener(this);

        disable = (Button)findViewById(R.id.btnDisable);
        enable =(Button)findViewById(R.id.btnEnable);
        disable.setOnClickListener(this);
        enable.setOnClickListener(this);
    }

 @Override
 public void onClick(View v) {

  if(v == lock){
    boolean active = deviceManger.isAdminActive(compName);
             if (active) {
                 deviceManger.lockNow();
             }
  }

  if(v == enable){
   Intent intent = new Intent(DevicePolicyManager
     .ACTION_ADD_DEVICE_ADMIN);
            intent.putExtra(DevicePolicyManager.EXTRA_DEVICE_ADMIN,
                    compName);
            intent.putExtra(DevicePolicyManager.EXTRA_ADD_EXPLANATION,
                    "Additional text explaining why this needs to be added.");
            startActivityForResult(intent, RESULT_ENABLE);
  }

  if(v == disable){
     deviceManger.removeActiveAdmin(compName);
              updateButtonStates();
  }  
 }

 private void updateButtonStates() {

        boolean active = deviceManger.isAdminActive(compName);
        if (active) {
            enable.setEnabled(false);
            disable.setEnabled(true);

        } else {
            enable.setEnabled(true);
            disable.setEnabled(false);
        }    
 }

  protected void onActivityResult(int requestCode, int resultCode, Intent data) {
         switch (requestCode) {
             case RESULT_ENABLE:
                 if (resultCode == Activity.RESULT_OK) {
                     Log.i("DeviceAdminSample", "Admin enabled!");
                 } else {
                     Log.i("DeviceAdminSample", "Admin enable FAILED!");
                 }
                 return;
         }
         super.onActivityResult(requestCode, resultCode, data);
     }
}

MyAdmin.java

    package com.kns;
import android.app.admin.DeviceAdminReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.SharedPreferences;
import android.widget.Toast;

public class MyAdmin extends DeviceAdminReceiver{


    static SharedPreferences getSamplePreferences(Context context) {
        return context.getSharedPreferences(
          DeviceAdminReceiver.class.getName(), 0);
    }

    static String PREF_PASSWORD_QUALITY = "password_quality";
    static String PREF_PASSWORD_LENGTH = "password_length";
    static String PREF_MAX_FAILED_PW = "max_failed_pw";

    void showToast(Context context, CharSequence msg) {
        Toast.makeText(context, msg, Toast.LENGTH_SHORT).show();
    }

    @Override
    public void onEnabled(Context context, Intent intent) {
        showToast(context, "Sample Device Admin: enabled");
    }

    @Override
    public CharSequence onDisableRequested(Context context, Intent intent) {
        return "This is an optional message to warn the user about disabling.";
    }

    @Override
    public void onDisabled(Context context, Intent intent) {
        showToast(context, "Sample Device Admin: disabled");
    }

    @Override
    public void onPasswordChanged(Context context, Intent intent) {
        showToast(context, "Sample Device Admin: pw changed");
    }

    @Override
    public void onPasswordFailed(Context context, Intent intent) {
        showToast(context, "Sample Device Admin: pw failed");
    }

    @Override
    public void onPasswordSucceeded(Context context, Intent intent) {
        showToast(context, "Sample Device Admin: pw succeeded");
    } 

} 

main.xml

    <textview android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="To Lock Screen First Enable it.." android:textsize="15sp"></textview>

    <button android:id="@+id/lock" android:layout_width="match_parent" android:layout_height="wrap_content" android:text="Lock The Phone"></button>

    <button android:id="@+id/btnEnable" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="Enable"></button>

    <button android:id="@+id/btnDisable" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="Disable"></button></linearlayout>

policies.xml

<?xml version="1.0" encoding="utf-8"?>
<device-admin xmlns:android="http://schemas.android.com/apk/res/android">
    <uses-policies>
        <limit-password>
        <watch-login>
        <reset-password>
        <force-lock>
        <wipe-data>
    </wipe-data></force-lock></reset-password></watch-login></limit-password></uses-policies>
</device-admin>

You can have this policies.xml either in layout or in xml folder. Only thing you need to take care is metadata tag in Androidmanifest file.

 <?xml version="1.0" encoding="utf-8"?>
    <manifest xmlns:android="http://schemas.android.com/apk/res/android" package="com.kns" android:versioncode="1" android:versionname="1.0">
        <uses-sdk android:minsdkversion="8">

        <application android:icon="@drawable/icon" android:label="@string/app_name">
            <activity android:name=".LockScreenActivity" android:label="@string/app_name">
                <intent-filter>
                    <action android:name="android.intent.action.MAIN">
                    <category android:name="android.intent.category.LAUNCHER">
                </category></action></intent-filter>
            </activity>
 <receiver android:name=".MyAdmin" android:permission="android.permission.BIND_DEVICE_ADMIN">
     <meta-data android:name="android.app.device_admin" android:resource="@layout/policies">
                    <intent-filter>
         <action android:name="android.app.action.DEVICE_ADMIN_ENABLED">
                        </action></intent-filter>
                    </meta-data></receiver>
 </application>
        </uses-sdk></manifest>

Before Lock the screen you need to Enable Admin Permission

Then you will get this..

After Enable you will lock screen..like this