IMPORTANT: Remember to add your package name before you copy and paste this java code into the JustJava app's MainActivity.java file.

MainActivity.java

/**
 * IMPORTANT: Make sure you are using the correct package name. 
 * This example uses the package name:
 * package com.example.android.justjava
 * If you get an error when copying this code into Android studio, update it to match teh package name found
 * in the project's AndroidManifest.xml file.
 **/
 
 package com.example.android.justjava; 
 


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

/**
 * This app displays an order form to order coffee.
 */
public class MainActivity extends AppCompatActivity {

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

    /**
     * This method is called when the order button is clicked.
     */
    public void submitOrder(View view) {
        display(1);
    }

    /**
     * This method displays the given quantity value on the screen.
     */
    private void display(int number) {
        TextView quantityTextView = (TextView) findViewById(R.id.quantity_text_view);
        quantityTextView.setText("" + number);
    }
}

Modify activity_main.xml to add this Button XML attribute.
android:onClick = "submitOrder"
Replace entire MainActivity.java file with the file provided in the link to the code.
Run app on device.
What happens when you click on the Button?
Solution

1. I modify activity_main.xml to onclick attribute
2. I copy the MainActivity.java by new version ,then I click to run,it display nicely
3. it update the quantity value one
   I still didn't get the answer of the question ? Help Help

fun main()
{
mood == "happy" && weather == "Sunny" -> "go for a walk"
else -> "Stay home and read."
if else->
whatShouldIDoToday("sad")
}

Create a program that suggests an activity based on various parameters.

1. Start in a new file with a main function.
2. From main(), create a function, whatShouldIDoToday().
3. Let the function have three parameters.
   mood: a required string parameter
   weather: a string parameter that defaults to "sunny"
   temperature: an Integer parameter that defaults to 24 (Celsius).
4. Use a when construct to return some activities based on combinations of conditions. For example:
   mood == "happy" && weather == "Sunny" -> "go for a walk"
   else -> "Stay home and read."
5. Copy/paste your finished function into REPL, and call it with combinations of arguments. For example:
   whatShouldIDoToday("sad")

Stay home and read.

fun describe(obj: Any): String =when(mood == "happy" && weather == "Sunny" -> "go for a walk")
{
mood -> "happy"
"sunny" -> "Go for a walk"
weather -> "Stay home and read."
else -> whatShouldIDoToday("Sad")
}
fun main() {
println(describe(happy))
println(describe("sunny"))
println(describe(weather))
println(describe("WhatShouldIDoToday"))

}

//The output is //
Go for a walk
Stay home and read.
Sad