// Array of ints:
int[] lottoNumbers;
// Array of Strings:
String[] clothingItems;
// Array of ints:
int[] lottoNumbers = {12, 29, 4, 38, 3};
// Array of Strings:
String[] clothingItems = {"Huipil", "Beanie", "Kimono", "Sari"};
//
String[] menuItems = new String[5];
menuItems[0] = "Grilled Chicken Fajita";
menuItems[1] = "Fried Plantains";
menuItems[2] = "Black Bean Taco";
menuItems[3] = "Chili Nachos";
menuItems[4] = "Chorizo Burrito";

String[] clothingItems = {"Huipil", "Beanie", "Kimono", "Sari"};
System.out.println(clothingItems[2]); // Prints: Kimono

String[] clothingItems = {"Huipil", "Beanie", "Kimono", "Sari"};
// Change element value:
clothingItems[1] = "Sweater";
System.out.println(clothingItems[1]); // Prints: Sweater

int[] lottoNumbers = {12, 29, 4, 38, 3};
System.out.println(lottoNumbers.length); // Prints: 5

//第一种方法
int[] lottoNumbers = {12, 29, 4, 38, 3};
for (int i = 0; i < lottoNumbers.length; i++) {
  // Output the current index value:
  System.out.println(lottoNumbers[i]);
}
/*
Prints:
12
29
4
38
3
*/
//第二种方法
int[] lottoNumbers = {12, 29, 4, 38, 3};
for (int num: lottoNumbers) {
  System.out.println(num);
}
/*
Prints:
12
29
4
38
3
*/

// 2D int array
int[][] nums;
int[][] nums = {{10, 9, 8}, {7, 6, 5}, {4, 3, 2}};
//
int[][] intArray = new int[2][3];
intArray[0][0] = 1;
intArray[0][1] = 2;
intArray[0][2] = 4;
intArray[1][0] = 1;
intArray[1][1] = 3;
intArray[1][2] = 6;

int[][] nums = {{10, 9, 8}, {7, 6, 5}, {4, 3, 2}}; 
// Within the first array, access the second element:
System.out.println(nums[0][1]); // Prints: 9

char[][] letters = {{'A', 'a'}, {'B', 'x'}, {'C', 'c'}};
// Update the value:
letters[1][1] = 'b';
System.out.println(letters[1][1]); // Prints: b

char[][] letters = {{'A', 'a'}, {'B', 'b'}, {'C', 'c'}};
for (int i = 0; i < letters.length; i++){
  for (int j = 0; j < letters[0].length; j++){
    System.out.print(letters[i][j]);
  }
}
// Prints: AaBbCc
char[][] letters = {{'A', 'a'}, {'B', 'b'}, {'C', 'c'}};
for (int i = 0; i < letters[0].length; i++){
  for (int j = 0; j < letters.length; j++){
    System.out.print(letters[j][i]);
  }
}
// Prints: ABCabc

类和构造函数

access modifiers 访问修饰符

构造函数：用来创建对象

public class Car {
  public Car() {
    // Instructions for creating a Car instance
       System.out.println("I'm a constructor!");
  }
  public static void main(String[] args) {
    // Invoke the constructor:
    Car ferrari = new Car();  // Prints: I'm a constructor! 
  }
}

class Cat {
  String noise;
  int numLives = 9;
  public String toString() {
    System.out.println("The cat with " + numLives + " lives says " + noise);
  }
  public Cat(String animalNoise){
    noise = animalNoise;
  }
  public static void main(String[] args) {
    Cat myCat = new Cat("mew");
    System.out.println(myCat); // Prints: The cat with 9 lives says mew
  }
}

class Shape {
  Shape() {
    System.out.println("I am a shape!");
  }
}
// Make Triangle a subclass of Shape:
class Triangle extends Shape {
  Triangle() {
    System.out.print("I am a triangle!");
  }
  public static void main(String[] argos) {
    Shape sq = new Shape(); // Prints: I am a shape!
    Triangle tri = new Triangle();
    /* Prints:
    I am a shape!
    I am a triangle!
    */
  }
}
------------------------------------------------------------------
class Shape {
  int numSides;
  Shape(int numSides) {
    this.numSides = numSides;
  }
}
class Triangle extends Shape {
  Triangle() {
    // Use super() to call the Shape constructor:
    super(3);
  }
  public static void main(String[] args) {
    Shape sq = new Shape(4);
    Triangle tri = new Triangle();
    System.out.println(sq.numSides); // Prints: 4
    System.out.println(tri.numSides); // Prints: 3
  }
}
--------------------------------------------------------------------
class Pho extends Noodle {
  public Pho() {
    super("flat");
  }
}
class Noodle {
  boolean isCooked = false;
  String shape;
  public Noodle(String shape) {
     this.shape = shape;
  }
  public static void main(String[] args) {
     Pho lunch = new Pho();
     System.out.println(lunch.shape);
     System.out.println(lunch.isCooked);
  }
}

多态 继承的同时还保留自己的功能

// Parent class:
class Bird {
  public Bird() {
    // Instructions for creating a Bird go here:
  }
  public void move() {
    System.out.println("The bird flies away");
  }
}
// Child class:
class Flamingo extends Bird {
  public Flamingo() {
    // Instructions for creating a Flamingo go here:
  }
  public static void main(String[] args) {
     Flamingo myFlamingo = new Flamingo();
     myFlamingo.move(); // The bird flies away
  }
}

// Parent class:
class Bird {
  public Bird() {
    // Instructions for creating a Bird go here:
  }
  public void move() {
    System.out.println("The bird flies away");
  }
}
// Child class:
class Penguin extends Bird {
  public Penguin() {
    // Instructions for creating a Penguin go here:
  }
  // Override the parent class method:
  @Override
  public void move() {
    System.out.println("The penguin waddles away");
  }
  public static void main(String[] args) {
    Penguin myPenguin = new Penguin();
    myPenguin.move(); // Prints: The penguin waddles away
  }
}

class Vet {
  public void Vet() {
    // Instructions for instance go here:
  }
  public void getCheckUp(Animal patient) {
    // Instructions for method go here:
  }
  public void main(String[] args) {
    // Create a Vet object
    Vet catDoctor = newVet();
    // Create an Animal object
    Animal myCat = new Cat();
    // Send Animal object as a parameter for a Vet method:
    catDoctor.getCheckUp(myCat);
  }
}

class BankAccount {
  protected double balance;
  public BankAccount(double balanceIn){
    balance = balanceIn;
  }
  public void printBalance() {
    System.out.println("Your account balance is $" + balance);
  }
}
class CheckingAccount extends BankAccount {
  public CheckingAccount(double balance) {
    super(balance);
  }
  @Override
  public void printBalance() {
    System.out.println("Your checking account balance is $" + balance);
  }
  public static void main(String[] args) {
    BankAccount myCheckings = new CheckingAccount(5000);
    myCheckings.printBalance();
  }
}
//print Your checking account balance is $5000.0