How to add TIMESTAMP in the Android Studio CalcApp?

Question

↓based on the link below. History for simple calculator - Android

Trying to add a timestamp when clicking the "=" button. I am not sure is this working correctly?

My final goal is that,

・Save calculation history into the History array with TIMESTAMP when the user clicks the "=" button.

MainActivity.java

package com.example.kaguya;

import androidx.appcompat.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import java.sql.Timestamp;
import java.util.ArrayList;
import java.util.List;
import java.lang.String;
import android.os.Bundle;

public class MainActivity<format> extends AppCompatActivity {

    Button b0, b1, b2, b3, b4, b5, b6, b7, b8, b9, bplus, bminus, bmulti, bdiv, beq, bc, hh;
    List<String> history= new ArrayList<>();
    String timestamp = new String(String.valueOf(System.currentTimeMillis()));
    EditText edit1;
    TextView hist;
    int nr1, nr2;
    boolean plus, minus, multi, div;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        b0 = (Button) findViewById(R.id.b0);
        b1 = (Button) findViewById(R.id.b1);
        b2 = (Button) findViewById(R.id.b2);
        b3 = (Button) findViewById(R.id.b3);
        b4 = (Button) findViewById(R.id.b4);
        b5 = (Button) findViewById(R.id.b5);
        b6 = (Button) findViewById(R.id.b6);
        b7 = (Button) findViewById(R.id.b7);
        b8 = (Button) findViewById(R.id.b8);
        b9 = (Button) findViewById(R.id.b9);
        hh = (Button) findViewById(R.id.hh);
        bplus = (Button) findViewById(R.id.bplus);
        bminus = (Button) findViewById(R.id.bminus);
        bmulti = (Button) findViewById(R.id.bmulti);
        bdiv = (Button) findViewById(R.id.bdiv);
        bc = (Button) findViewById(R.id.bc);
        beq = (Button) findViewById(R.id.beq);
        edit1 = (EditText) findViewById(R.id.edit1);
        hist = (TextView) findViewById(R.id.hist);

        b0.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                edit1.setText(edit1.getText() + "0");
            }
        });

        b1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                edit1.setText(edit1.getText() + "1");
            }
        });

        b2.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                edit1.setText(edit1.getText() + "2");
            }
        });

        b3.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                edit1.setText(edit1.getText() + "3");
            }
        });

        b4.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                edit1.setText(edit1.getText() + "4");
            }
        });

        b4.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                edit1.setText(edit1.getText() + "4");
            }
        });

        b5.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                edit1.setText(edit1.getText() + "5");
            }
        });

        b6.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                edit1.setText(edit1.getText() + "6");
            }
        });

        b7.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                edit1.setText(edit1.getText() + "7");
            }
        });
        b8.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                edit1.setText(edit1.getText() + "8");
            }
        });

        b9.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                edit1.setText(edit1.getText() + "9");
            }
        });

        bplus.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if (edit1 == null){
                    edit1.setText("");
                }else {
                    nr1 = Integer.parseInt(edit1.getText() + "");
                    plus= true;
                    edit1.setText(null);
                }
            }
        });

        bminus.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                nr1 = Integer.parseInt(edit1.getText() + "");
                minus = true ;
                edit1.setText(null);
            }
        });

        bmulti.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                nr1 = Integer.parseInt(edit1.getText() + "");
                multi = true ;
                edit1.setText(null);
            }
        });

        bdiv.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                nr1 = Integer.parseInt(edit1.getText()+"");
                div = true ;
                edit1.setText(null);
            }
        });

        bc.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                edit1.setText("");
            }
        });


        beq.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                nr2 = Integer.parseInt(edit1.getText() + "");
                double res = 0;
                String res2 = timestamp;
                if (plus == true){
                    res = nr1 + nr2;
                    res2 = timestamp;
                    edit1.setText(nr1 + nr2+"");
                    plus=false;
                }

                if (minus == true){
                    res = nr1 - nr2;
                    res2 = timestamp;
                    edit1.setText(nr1 - nr2+"");
                    minus=false;
                }

                if (multi == true){
                    res = nr1 * nr2;
                    res2 = timestamp;
                    edit1.setText(nr1 * nr2+"");
                    multi=false;
                }

                if (div == true){
                    res = nr1 / nr2;
                    res2 = timestamp;
                    edit1.setText(nr1 / nr2+"");
                    div=false;
                }
                history.add(String.valueOf(res));
                history.add(String.valueOf(res2));
            }
        });

        hh.setOnClickListener(new View.OnClickListener() {
            int index = 0;
            public void onClick(View v) {
                history.get(index);
            }
        });
    }
}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:weightSum="1">


    <TextView
        android:layout_width="match_parent"
        android:id="@+id/hist"
        android:layout_height="100dp" />

    <EditText
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/edit1" />

    <GridLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_weight="1.10"
        android:id="@+id/GridLayout">

        <Button
            android:text="5"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/b5"
            android:layout_row="1"
            android:layout_column="1"/>

        <Button
            android:text="6"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/b6"
            android:layout_row="1"
            android:layout_column="2"/>

        <Button
            android:text="-"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/bminus" />

        <Button
            android:text="7"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/b7"
            android:layout_row="2"
            android:layout_column="0"/>

        <Button
            android:text="8"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/b8"
            android:layout_row="2"
            android:layout_column="1" />

        <Button
            android:text="9"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/b9"
            android:layout_row="2"
            android:layout_column="2" />

        <Button
            android:text="*"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/bmulti"
            android:layout_row="2"
            android:layout_column="3" />

        <Button
            android:text="+"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/bplus"
            android:layout_row="0"
            android:layout_column="3" />

        <Button
            android:text="3"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/b3"
            android:layout_row="0"
            android:layout_column="2" />

        <Button
            android:text="4"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/b4"
            android:layout_row="1"
            android:layout_column="0" />

        <Button
            android:text="0"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/b0"
            android:layout_row="3"
            android:layout_column="1" />

        <Button
            android:text="2"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/b2"
            android:layout_row="0"
            android:layout_column="1" />

        <Button
            android:text="1"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/b1"
            android:layout_row="0"
            android:layout_column="0" />

        <Button
            android:text="/"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/bdiv"
            android:layout_row="3"
            android:layout_column="3" />

        <Button
            android:text="="
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/beq"
            android:layout_row="3"
            android:layout_column="2" />

        <Button
            android:text="C"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/bc"
            android:layout_row="3"
            android:layout_column="0" />

        <Button
            android:id="@+id/bc2"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_row="3"
            android:layout_column="0"
            android:text="C" />

        <Button
            android:id="@+id/hh"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_row="4"
            android:layout_column="0"
            android:text="History" />

    </GridLayout>

</LinearLayout>

Answer 1

If you want to store history, you can use a database (which is recommended).

If the hosting is temporary, sharedpreferences may be used.

Some databases for your reference:

• Sqlite

• Realm

• Room

When storing a timestamp, you can treat it as an Integer (or Long) or String when storing.

To get the current timestamp, you can use this command.

Long tsLong = System.currentTimeMillis () / 1000;
String ts = tsLong.toString ();

Reference: Android Get Current timestamp?