在Java中填充Map的最有效方法

Question

I am new to Java and I'm coding a simple "Positive Quotes" app. (using Android Studio) that lets you press on a button, that will display a positive quote (randomly selected) from a Map.

The code itself is rather basic:

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

        // Sets the right TextView / Button to each object
        final TextView textView = (TextView)findViewById(R.id.textView);
        final Button button1 =  (Button)findViewById(R.id.button);

        // Implement listener for your button so that when you click the
        // button, android will listen to it.
        button1.setOnClickListener(new View.OnClickListener() {
            public void onClick(View v) {
                Map<Integer, String> quotes = new HashMap<Integer, String>();
                // Generate your quotes Map
                quotes = createQuotesMap();

                Random generator = new Random();
                Object[] values = quotes.values().toArray();
                Object randomValue = (String) values[generator.nextInt(values.length)];
                // Perform action on click
                textView.setText(randomValue.toString());
            }         });
    }

But my question comes from where I fill up my quotes map:

 public Map<Integer, String> createQuotesMap() {
        Map<Integer, String> quotes = new HashMap<Integer, String>();

        quotes.put(1, "Correction does much, but encouragement does more.");
        quotes.put(2, "Keep your face to the sunshine and you cannot see a shadow.");
        quotes.put(3, "Once you replace negative thoughts with positive ones, you'll start having positive results.");
        quotes.put(4, "Positive thinking will let you do everything better than negative thinking will.");
        quotes.put(5, "Pessimism leads to weakness, optimism to power.");
        quotes.put(6, "The thing that lies at the foundation of positive change, the way I see it, is service to a fellow human being.");
        quotes.put(7, "In every day, there are 1,440 minutes. That means we have 1,440 daily opportunities to make a positive impact.");
        quotes.put(8, "Attitude is a little thing that makes a big difference.");
        return quotes;
}

Would there be a more efficient way of filling up my Map, or a better container for such a basic application? Could you also point out bad coding habits from the chunk of code that I have shared?

EDIT:

My app. is now complete - I create an array of quotes (only once and not at every click like before) and display one, randomly chosen.

Answer 1

Hint: the main performance aspects here are:

1. You do not want to create a new map for each new users. The quotes will be be the same all the time, right; so the one and only thing worth worrying about is: how to make sure that you create the map exactly once. So instead of using a local variable, you could create a single static class-wide map.
2. Why do you want to use a map? You know, when you want to have a sequence of ints to be your key; why don't you just use an List?

In other words: when "optimizing" always try think about the big picture. But your question implies that you are very much thinking from the opposite side of things. You spent your time worrying about the cost of a single operation; instead of looking at your application at a hole ... Same thing for the map versus list thing. There is absolutely no point in using a map ... to then use it like an list.

Answer 2

Firstly, in terms of efficiency, instead of generating the map every time you click the button, consider making it a field of your Activity and initiating it in your onCreate() . You can then use that field in your onClickListener as such:

 //Class field
 private Map<Integer, String> quotes; 

 protected void onCreate(Bundle savedInstanceState) {

        // Generate your quotes Map 
        quotes = createQuotesMap();

        button1.setOnClickListener(new View.OnClickListener() {
            public void onClick(View v) {
                Random generator = new Random();
                Object[] values = quotes.values().toArray();
                //etc
            }         
        });
    }

Secondly and most importantly, this really doesn't warrant the use of a Map . You are better off using a simple array or an ArrayList .

You can still access random elements from them by using array[myRandomIndex] or arrayList.get(myRandomIndex) depending on how you wish to implement it.

Just be mindful that initialising these arrays should not be done in an OnClickListener as it would run that code every time the button is clicked.

Answer 3

You can create an array once using the method createQuotes() . And you don't need a map, because you only need to obtain a random string among the given strings. As for the key in the map, it transforms perfectly into the array's index. So I suggest you use the below :

public class YourClass {

    private static final String[] QUOTES = createQuotes();
    private Random generator = new Random();

    protected void onCreate(Bundle savedInstanceState) {
        // ...
        button1.setOnClickListener(new View.OnClickListener() {
            public void onClick(View v) {
                String randomValue = QUOTES[generator.nextInt(QUOTES.length)];
                textView.setText(randomValue);
            }         
        });
    }

    private static String[] createQuotes() {
        String[] quotes = new String[] {
                "Correction does much, but encouragement does more.",
                "Keep your face to the sunshine and you cannot see a shadow.",
                "Once you replace negative thoughts with positive ones, you'll start having positive results.",
                "Positive thinking will let you do everything better than negative thinking will.",
                "Pessimism leads to weakness, optimism to power.",
                "The thing that lies at the foundation of positive change, the way I see it, is service to a fellow human being.",
                "In every day, there are 1,440 minutes. That means we have 1,440 daily opportunities to make a positive impact.",
                "Attitude is a little thing that makes a big difference."
        }
        return quotes;
    }
}

I can't test the code. Please edit me if there's any error.

Answer 4

String[] quotes = {
"Correction does much, but encouragement does more.",
"Keep your face to the sunshine and you cannot see a shadow.",
"Once you replace negative thoughts with positive ones, you'll start having positive results.",

};

public void onClick(View v){

    ...

    Random r = new Random();
    selectedQuote = r.nextInt(quotes.length);
    textView.setText(selectedQuite);
    ...

}

I hope this helps you solve yout problem

Answer 5

String[] stringQuotes = {
"Correction does much, but encouragement does more.",
"Keep your face to the sunshine and you cannot see a shadow.",
"Once you replace negative thoughts with positive ones, you'll start having positive results.",
"Positive thinking will let you do everything better than negative thinking will."
};

for(int i = 0; i < stringQuotes.length; i++){
    quotes.put(i, stringQuotes[i]);
}

It is faster to use a for-loop, but it requires that all strings are saved in a string[] array which makes the initialization faster