NPE: Attempt to invoke virtual method 'android.content.pm.ApplicationInfo android.content.Context.getApplicationInfo()' on a null object reference

Question

I've this basic app called Navigation that I was trying to make to understand some concepts where there are 2 activities MainActivity and ActivityB MainActivity has a textview and a button to go on to ActivityB and ActivityB has an edit text and a button to go back to MainActivity editText takes string and string gets send to MainActivity and gets displayed in it's TextView

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I am Getting this Error :

Navigation keeps stopping

Here is stacktrace from logcat

2022-05-13 21:51:01.139 6899-6899/com.example.navigation E/AndroidRuntime: FATAL EXCEPTION: main Process: com.example.navigation, PID: 6899 java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.navigation/com.example.navigation.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.pm.ApplicationInfo android.content.Context.getApplicationInfo()' on a null object reference at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3545) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3792) at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:103) at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135) at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2210) at android.os.Handler.dispatchMessage(Handler.java:106) at android.os.Looper.loopOnce(Looper.java:201) at android.os.Looper.loop(Looper.java:288) at android.app.ActivityThread.main(ActivityThread.java:7839) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:548) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1003) Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.pm.ApplicationInfo android.content.Context.getApplicationInfo()' on a null object reference at android.content.ContextWrapper.getApplicationInfo(ContextWrapper.java:181) at android.view.ContextThemeWrapper.getTheme(ContextThemeWrapper.java:174) at android.content.Context.obtainStyledAttributes(Context.java:804) at androidx.appcompat.app.AppCompatDelegateImpl.createSubDecor(AppCompatDelegateImpl.java:848) at androidx.appcompat.app.AppCompatDelegateImpl.ensureSubDecor(AppCompatDelegateImpl.java:815) at androidx.appcompat.app.AppCompatDelegateImpl.findViewById(AppCompatDelegateImpl.java:640) at androidx.appcompat.app.AppCompatActivity.findViewById(AppCompatActivity.java:259) at com.example.navigation.MainActivity.(MainActivity.java:21) at java.lang.Class.newInstance(Native Method) at android.app.AppComponentFactory.instantiateActivity(AppComponentFactory.java:95) at androidx.core.app.CoreComponentFactory.instantiateActivity(CoreComponentFactory.java:45) at android.app.Instrumentation.newActivity(Instrumentation.java:1273) at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3532) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3792)  at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:103)  at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)  at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2210)  at android.os.Handler.dispatchMessage(Handler.java:106)  at android.os.Looper.loopOnce(Looper.java:201)  at android.os.Looper.loop(Looper.java:288)  at android.app.ActivityThread.main(ActivityThread.java:7839)  at java.lang.reflect.Method.invoke(Native Method)  at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:548)  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1003)  2022-05-13 21:51:01.209 6899-6899/? I/Process: Sending signal. PID: 6899 SIG: 9

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Here is the code for MainActivity :

package com.example.navigation;

import androidx.activity.result.ActivityResult;
import androidx.activity.result.ActivityResultCallback;
import androidx.activity.result.ActivityResultLauncher;
import androidx.activity.result.contract.ActivityResultContracts;
import androidx.annotation.Nullable;
import androidx.appcompat.app.AppCompatActivity;

import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

import com.example.navigation.ActivityB;

public class MainActivity extends AppCompatActivity {

    private TextView display_textview = findViewById(R.id.display_textview);

    ActivityResultLauncher<Intent> startForResult = registerForActivityResult(new ActivityResultContracts.StartActivityForResult(), new ActivityResultCallback<ActivityResult>() {

        @Override
        public void onActivityResult(ActivityResult result) {
            if (result == null || result.getResultCode() != RESULT_OK) {
                if (result.getData() != null && result.getData().getStringExtra("name") != null){
                    display_textview.setText(result.getData().getStringExtra("name"));
                }
            }
        }
    });

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        Button activityB_button = findViewById(R.id.activityB_button);

        activityB_button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {    //onClick method
                Intent intent = new Intent(MainActivity.this, ActivityB.class);
                startForResult.launch(intent);
            }
        });
    }
}

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Here is the code for ActivityB :

package com.example.navigation;

import androidx.appcompat.app.AppCompatActivity;

import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

public class ActivityB extends AppCompatActivity {

    private EditText edittext_activityB = findViewById(R.id.edittext_activityB);
    private Button activityA_button = findViewById(R.id.activityA_button);

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_b);

        activityA_button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                //extracting data from editText
                String personName = edittext_activityB.getText().toString();
                Intent intent = new Intent();
                intent.putExtra("name", personName);
                setResult(RESULT_OK, intent);
                finish();
            }
        });

    }
}

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As far as i can understand logcat says :at com.example.navigation.MainActivity.(MainActivity.java:21)

So maybe this line "private TextView display_textview = findViewById(R.id.display_textview);"

has some issue.

Do tell me If you need any other info. I am most active at : Instagram : @chimtubhaiya you can directly dm me there :)

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Thanks to all who tried to solve my issue :)