Gets the value of index 0

a[0]
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for (int i = 0; i < a.length; i++) {
	a[i];
}
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Exercise: Randomly generate a bicolor ball

Two-color ball game rules there are 6 groups of red ball, each group from 1 to 33 to draw one, six do not repeat each other. And then the blue ball takes a number from 1 to 16, and this whole thing makes up the bicolor ball

xml

    <Button
        android:id="@+id/button"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Randomly generate bicolor balls." />

    <TextView
        android:id="@+id/red"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:gravity="center"
        android:textColor="#FF0000"
        android:textSize="18sp" />

    <TextView
        android:id="@+id/blue"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:gravity="center"
        android:textColor="#0000FF"
        android:textSize="18sp" />
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public class MainActivity extends AppCompatActivity implements View.OnClickListener {
    Button button;
    TextView redText;
    TextView blueText;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        button = findViewById(R.id.button);
        button.setOnClickListener(this);
    }

    @Override
    public void onClick(View v) {
        int[] r = new int[33];
        int[] b = new int[16];
        for (int i = 0; i < 33; i++) {
            r[i] = i + 1;
        }
        for (int i = 0; i < 16; i++) {
            b[i] = i + 1;
        }
        // Convert the array to String output
        Log.d("Bicolor"."Red:" + Arrays.toString(r));
        Log.d("Bicolor"."Blue" + Arrays.toString(b));

        // Red ball result array and tag array
        int[] red = new int[6];
        boolean[] flag = new boolean[33];

        for (int i = 0; i < 6; i++) {
            int j;
            do {
                // select a random subscript from the r array and assign it to
                j = new Random().nextInt(33);
            } while (flag[j]);// If yes, re-select
            red[i] = r[j];
            flag[j] = true;
        }

        // The result array
        int blue = b[new Random().nextInt(16)];
        // Display the result in two TextViews
        redText = findViewById(R.id.red);
        blueText = findViewById(R.id.blue);

        redText.setText("Red ball:" + Arrays.toString(red));
        blueText.setText("Basketball:"+ blue); }}Copy the code

Run the program and the results are as follows;

Practice: Guess letters

public class Main {
    public static void main(String[] args) {
        // Randomly generate 5 unrepeated uppercase letters
        char[] s = random();

        System.out.println("5 unrepeated uppercase letters have been generated");

        while (true) {
            System.out.println("Guess");
            // Get the string entered by the user
            String input = new Scanner(System.in).nextLine();
            // To compare with the array above, convert the string to an array of characters
            char[] inputResult = input.toCharArray();

            String result = compare(inputResult, s);
            System.out.println(result);
            // If the result is "5A0B", the end
            if (result.equals("5A0B")) {
                break; }}}static char[] random() {
        // Create a char array of length 26
        char[] c = new char[26];
        // Insert A-Z in order
        for (int i = 0; i < c.length; i++) {
            c[i] = (char) ('A' + i);
        }
        // Visit the first five locations. The purpose of this step is to transpose the first five letters and the next five letters to produce non-repeating letters
        for (int i = 0; i < 5; i++) {
            int j = i + new Random().nextInt(26 - i);
            char temp = c[i];
            c[i] = c[j];
            c[j] = temp;
        }
        System.out.println(Arrays.toString(c));
        // Cut the first five letters to form a new array
        char[] result = Arrays.copyOf(c, 5);
        System.out.println("The first five letters after the interception:" + Arrays.toString(result));
        return result;
    }


    static String compare(char[] input, char[] result) {
        int a = 0;
        int b = 0;
        for (int i = 0; i < 5; i++) {
            for (int j = 0; j < 5; j++) {
                if (input[i] == result[j]) {
                    if (i == j) {
                        // Letters are equal and positions are equal
                        a++;
                    } else {
                        // The letters are equal, but the positions are different
                        b++;
                    }
                    // There are 5 different letters, so if you find the same one, break
                    break; }}}return a + "A" + b + "B"; }}Copy the code

Running result:

A two-dimensional array is an array that stores a one-dimensional array (memory address/reference)

Create an array

int[][] a = new int[3] [2];
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2. The length of the outer array is 3, and each of the inner arrays is 2. 3. The memory address of an array is stored in the outer array

int[][] a = new int[3] [];Copy the code

A [0] = new int[5]; a[0] = new int[5]; A [1] = new int[]{5,3,7,4} a[2] = new int[]{5,3,7,4}

You can also assign values directly

int[][] a = {
	{2.1.5.6},
	{4.5},
	{2.4}};Copy the code

access

a[0] [1]
a[2] [0]
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traverse

for (int i = 0; i < a.length; i++) {
	for (int j = 0; j < a[i].length; j++) { System.out.println(a[i][j]); }}Copy the code