Question

I need the java code for a 4 function calculator app on android studio (do this on android studio) -

The requirements are the following :

- The only buttons needed are 0-9, *, /, +, -, a clear, and enter button

- Implement the onclicklistener on the main activity

- The calcuator should use order of operations (PEMDAS)

- It should be able to continue from a previous answer (Ex: If you type 2+6 the calculator will display 8. If you then multiple by 2 the current result will simply be multiplied by 2)

- It should read the entire sequence of numbers and operators and save them into a String. The information can be read out of the String using a StringTokenizer. The delimiters will be the operators on the calculator.

- The entire mathematical expression will be displayed on the screen before the equal button is clicked.

- The equation will simply be evaluated in the order that the user types in the numbers rather than the precedence

- If the user enters an equation with invalid syntax, the output should display “error”. The calculator should also display “error” for any mathematical calculations that are impossible.

Answer 1

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JAVA Code:

package com.example.10012698.calculatorproject;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

import java.util.ArrayList;
import java.util.StringTokenizer;
public class MainActivity extends AppCompatActivity implements View.OnClickListener {

Button button0, button1, button2, button3, button4, button5, button6,
button7, button8, button9, buttonadd, buttonsubtract, buttonmultiply,
buttondivide, buttonequals, buttonclear;
TextView display;
String displaytext="";
double result;
double x, y;
ArrayList<String> list;


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

button0 = (Button) findViewById(R.id.button0);
button1 = (Button) findViewById(R.id.button1);
button2 = (Button) findViewById(R.id.button2);
button3 = (Button) findViewById(R.id.button3);
button4 = (Button) findViewById(R.id.button4);
button5 = (Button) findViewById(R.id.button5);
button6 = (Button) findViewById(R.id.button6);
button7 = (Button) findViewById(R.id.button7);
button8 = (Button) findViewById(R.id.button8);
button9 = (Button) findViewById(R.id.button9);
buttonadd = (Button) findViewById(R.id.buttonadd);
buttonsubtract = (Button) findViewById(R.id.buttonsubtract);
buttonmultiply = (Button) findViewById(R.id.buttonmultiply);
buttondivide = (Button) findViewById(R.id.buttondivide);
buttonclear = (Button) findViewById(R.id.buttonclear);
buttonequals = (Button) findViewById(R.id.buttonequals);
display = (TextView) findViewById(R.id.display);
display.setOnClickListener(this);
list = new ArrayList<>();
}

public void onClick(View view)
{
if(!(view.equals(buttonclear)&&!(view.equals(buttonequals))))
{
display.setText(display.getText()+""+((Button)view).getText());

if(displaytext.equals("0"))
{
display.setText(" ");
}

if(view.equals(buttonclear))
{
display.setText(" ");
}

if(view.equals(buttonequals))
{
displaytext= displaytext.substring(0,displaytext.length()-1);
StringTokenizer operators= new StringTokenizer(displaytext, "+-*/",true);

while(operators.hasMoreTokens())
{
list.add(operators.nextToken());
}

for(int j=0; j<list.size()-1; j++)
{
if (list.get(j).equals("*") || list.get(j).equals("/"))
{
x = Double.parseDouble(list.get(j - 1));
y = Double.parseDouble(list.get(j + 1));

if (list.get(j).equals("*"))
{
result+=(x*y);
}

if (list.get(j).equals("/"))
{
result+=(x/y);
}
}
}
for(int k=0;k<list.size()-1;k++)
{
if (list.get(k).equals("+") || list.get(k).equals("-"))
{
x = Double.parseDouble(list.get(k - 1));
y = Double.parseDouble(list.get(k + 1));

if (list.get(k).equals("+"))
{
result+=(x+y);
}

if (list.get(k).equals("-"))
{
result+=(x-y);
}
}
}
}
display.setText(""+result);


}
}

XML Code:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity"
    android:orientation="vertical"
    android:weightSum="100">

    <TextView
        android:id="@+id/display"
        android:layout_width="match_parent"
        android:layout_height="0px"
        android:layout_weight="15"
        android:text=""
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="0px"
        android:layout_weight="20"
        android:orientation="horizontal"
        android:weightSum="100">

        <Button
            android:id="@+id/buttonadd"
            android:layout_width="0px"
            android:layout_height="match_parent"
            android:layout_weight="25"
            android:text="+"/>

        <Button
            android:id="@+id/button7"
            android:layout_width="0px"
            android:layout_height="match_parent"
            android:layout_weight="25"
            android:text="7"/>
        <Button
            android:id="@+id/button8"
            android:layout_width="0px"
            android:layout_height="match_parent"
            android:layout_weight="25"
            android:text="8"/>
        <Button
            android:id="@+id/button9"
            android:layout_width="0px"
            android:layout_height="match_parent"
            android:layout_weight="25"
            android:text="9"/>
    </LinearLayout>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="0px"
        android:layout_weight="20"
        android:orientation="horizontal"
        android:weightSum="100">

        <Button
            android:id="@+id/buttonsubtract"
            android:layout_width="0px"
            android:layout_height="match_parent"
            android:layout_weight="25"
            android:text="-"/>

        <Button
            android:id="@+id/button4"
            android:layout_width="0px"
            android:layout_height="match_parent"
            android:layout_weight="25"
            android:text="4"/>
        <Button
            android:id="@+id/button5"
            android:layout_width="0px"
            android:layout_height="match_parent"
            android:layout_weight="25"
            android:text="5"/>
        <Button
            android:id="@+id/button6"
            android:layout_width="0px"
            android:layout_height="match_parent"
            android:layout_weight="25"
            android:text="6"/>
    </LinearLayout>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="0px"
        android:layout_weight="20"
        android:orientation="horizontal"
        android:weightSum="100">

        <Button
            android:id="@+id/buttonmultiply"
            android:layout_width="0px"
            android:layout_height="match_parent"
            android:layout_weight="25"
            android:text="*"/>

        <Button
            android:id="@+id/button1"
            android:layout_width="0px"
            android:layout_height="match_parent"
            android:layout_weight="25"
            android:text="1"/>
        <Button
            android:id="@+id/button2"
            android:layout_width="0px"
            android:layout_height="match_parent"
            android:layout_weight="25"
            android:text="2"/>
        <Button
            android:id="@+id/button3"
            android:layout_width="0px"
            android:layout_height="match_parent"
            android:layout_weight="25"
            android:text="3"/>
    </LinearLayout>


    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="0px"
        android:layout_weight="20"
        android:orientation="horizontal"
        android:weightSum="100">

        <Button
            android:id="@+id/buttondivide"
            android:layout_width="0px"
            android:layout_height="match_parent"
            android:layout_weight="25"
            android:text="/"/>

        <Button
            android:id="@+id/buttonclear"
            android:layout_width="0px"
            android:layout_height="match_parent"
            android:layout_weight="25"
            android:text="Clear"/>
        <Button
            android:id="@+id/button0"
            android:layout_width="0px"
            android:layout_height="match_parent"
            android:layout_weight="25"
            android:text="0"/>
        <Button
            android:id="@+id/buttonequals"
            android:layout_width="0px"
            android:layout_height="match_parent"
            android:layout_weight="25"
            android:text="="/>
    </LinearLayout>
</LinearLayout>

Screenshot of the Output:

Please UPVOTE my answer if you find this explaination to be helpful !!