Java学习笔记 - 第017天

作者: 迷茫o | 来源:发表于2016-12-20 20:25 被阅读0次

每日要点

容器

容器(集合框架Container) - 承载其他对象的对象

Collection

List
ArrayList
LinkedList
Set

List

ArrayList - 底层实现是一个数组使用连续内存可以实现随机存取
List<String> list = new ArrayList<>();
LinkedList - 底层实现是一个双向循环链表可以使用碎片内存不能随机存取但是增删元素是需要修改引用即可所以增删元素时有更好的性能
List<String> list = new LinkedList<>();
从Java 5开始容器可以指定泛型参数来限定容器中对象引用的类型
带泛型参数的容器比不带泛型参数的容器中使用上更加方便
Java 7开始构造器后面的泛型参数可以省略 - 钻石语法

List<String> list = new ArrayList<String>();
List<String> list = new ArrayList<>();

Java 5
容器中只能放对象的引用不能放基本数据类型
所以向容器中添加基本数据类型时会自动装箱(auto-boxing)
所谓自动装箱就是将基本数据类型处理成对应的包装类型

list.add(1000); // list.add(new Integer(1000));
list.add(3.14); // list.add(new Double(3.14));
list.add(true); // list.add(new Boolean(true));

List接口普通方法:

增
list.add("apple");
根据索引添加对象:
list.add(list.size(), "shit");
删
list.remove("apple");
清空:
list.clear();
根据指定的参考系删除所有
list.removeAll(temp);
根据指定的参考系保留所有
list.retainAll(temp);
查
方法一:

        for (int i = 0; i < list.size(); i++) {
            System.out.println(list.get(i));
        }

方法二:

        for (Object object : list) {
            System.out.println(object.getClass());
        }

方法三:

        Iterator<String> iterator = list.iterator();
        while (iterator.hasNext()) {
            System.out.println(iterator.next());
        }

Java 8以后新特性
从Java 8开始可以给容器发送forEach消息对元素进行操作
orEach方法的参数可以是方法引用也可以是Lambda表达式
方法引用
list.forEach(System.out::println);
Lambda表达式

        list.forEach(e -> {
            System.out.println(e.toUpperCase());
        });

杂项

基本类型　　包装类型(Wrapper class)
byte 　　　　Byte ---> new Byte(1)
short 　　　　Short
int 　　　　　Integer
long 　　　　Long
float 　　　　Float
double 　　　Double
boolean 　　Boolean

例子

1.自动装箱和自动拆箱

        Object object1 = 100; // 自动装箱
        System.out.println(object1.getClass());
        Integer object2 = (Integer) object1;
        int a = object2;  // 自动拆箱
        int b = (Integer) object1;
        System.out.println(a);
        System.out.println(b);
        
        List<Integer> list = new ArrayList<>();
        for (int i = 0; i < 10; i++) {
            // 自动装箱(auto-boxing) int ---> Integer
            list.add((int) (Math.random() * 20));
        }
        for (Integer x : list) {   // int x : list
            // 自动拆箱(auto-unboxing) Integer对象 ---> int
            if (x > 10) {
                System.out.println(x);
            }
        }

2.面试题: Integer c = 123;　Integer d = 123;　是否相等

        int[] x = {1, 2, 3};
        int[] y = {1, 2, 3};
        System.out.println(x.hashCode());
        System.out.println(y.hashCode());
        System.out.println(x == y);
        // 数组没有重写equals方法
        System.out.println(x.equals(y));
        System.out.println(Arrays.equals(x, y));
        
        Integer a = 12345;
        Integer b = 12345;
        
        System.out.println(a == b);
        System.out.println(a.equals(b));
        
        // Integer 有准备 -128~127的常量
        Integer c = 123;
        Integer d = 123;
        
        System.out.println(c == d);
        System.out.println(c.intValue() == d.intValue());
        System.out.println(c.equals(d));

贪吃蛇

方向枚举:

public enum Direction {
    UP, RIGHT, DOWN, LEFT
}

蛇节点:

/**
 * 蛇节点
 * @author Kygo
 *
 */
public class SnakeNode {
    private int x;
    private int y;
    private int size;
    
    public SnakeNode(int x, int y, int size) {
        this.x = x;
        this.y = y;
        this.size = size;
    }
    
    public void draw(Graphics g) {
        g.fillRect(x, y, size, size);
        Color currentColor = g.getColor();
        g.setColor(Color.BLACK);
        g.drawRect(x, y, size, size);
        g.setColor(currentColor);
    }
    
    public int getX() {
        return x;
    }
    
    public int getY() {
        return y;
    }
    
    public int getSize() {
        return size;
    }
    
    public void setX(int x) {
        this.x = x;
    }
    
    public void setY(int y) {
        this.y = y;
    }
}

蛇类:

public class Snake {
    private List<SnakeNode> nodes;
    private Color color;
    private Direction dir;
    private Direction newDir;
    
    public Snake() {
        this(Color.GREEN);
    }
    
    public Snake(Color color) {
        this.color = color;
        this.dir = Direction.LEFT;
        this.nodes = new LinkedList<>();
        for (int i = 0; i < 5; i++) {
            SnakeNode node = new SnakeNode(300 + i * 20, 300, 20);
            nodes.add(node);
        }
    }
    
    public void move() {
        if (newDir != null) {
            dir = newDir;
            newDir = null;
        }
        SnakeNode head = nodes.get(0);
        int x = head.getX();
        int y = head.getY();
        int size = head.getSize();
        switch (dir) {
        case UP:
            y -= size;
            break;
        case RIGHT:
            x += size;
            break;
        case DOWN:
            y += size;
            break;
        case LEFT:
            x -= size;
            break;
        }
        SnakeNode newHead = new SnakeNode(x, y, size);
        nodes.add(0, newHead);
        nodes.remove(nodes.size() - 1);
    }
    
    public boolean eatEgg(SnakeNode egg) {
        if (egg.getX() == nodes.get(0).getX() && egg.getY() == nodes.get(0).getY()) {
            nodes.add(egg);
            return true;
        }
        return false;
    }
    
    public boolean die() {
        for (int i = 1; i < nodes.size(); i++) {
            if (nodes.get(0).getX() == nodes.get(i).getX() && nodes.get(0).getY() == nodes.get(i).getY()) {
                return true;
            }
        }
        return false;
    }
    
    public void draw(Graphics g) {
        g.setColor(color);
        for (SnakeNode snakeNode : nodes) {
            snakeNode.draw(g);
        }
    }
    
    public Direction getDir() {
        return dir;
    }
    
    public void setDir(Direction newDir) {
        if ((this.dir.ordinal() + newDir.ordinal()) % 2 != 0) {
            if (this.newDir == null) {
                this.newDir = newDir;   
            }       
        }
    }
}

贪吃蛇窗口:

public class SnakeGameFrame extends JFrame {
    private BufferedImage image = new BufferedImage(600, 600, 1);
    private Snake snake = new Snake();
    private SnakeNode egg = new SnakeNode(60, 60, 20);

    public SnakeGameFrame() {
        this.setTitle("贪吃蛇");
        this.setSize(600, 600);
        this.setResizable(false);
        this.setLocationRelativeTo(null);

        // 绑定窗口监听器
        this.addWindowListener(new WindowAdapter() {
            @Override
            public void windowClosing(WindowEvent e) {
                // Todo: 存档
                System.exit(0);
            }
        });
        // 绑定键盘事件监听器
        this.addKeyListener(new KeyAdapter() {
            @Override
            public void keyPressed(KeyEvent e) {
                int keyCode = e.getKeyCode();
                Direction newDir = null;
                switch (keyCode) {
                case KeyEvent.VK_W:
                    newDir = Direction.UP;
                    break;
                case KeyEvent.VK_D:
                    newDir = Direction.RIGHT;
                    break;
                case KeyEvent.VK_S:
                    newDir = Direction.DOWN;
                    break;
                case KeyEvent.VK_A:
                    newDir = Direction.LEFT;
                    break;
                }
                if (newDir != null && newDir != snake.getDir()) {
                    snake.setDir(newDir);
                }
            }
        });

        Timer timer = new Timer(200, e -> {
            snake.move();
            if (snake.eatEgg(egg)) {
                int x = (int) (Math.random() * 31) * 20;
                int y = (int) (Math.random() * 30 + 1) * 20;
                egg.setX(x);
                egg.setY(y);
            }
            if (snake.die()) {
                System.out.println("死了");
            }
            repaint();
        });
        timer.start();
    }

    @Override
    public void paint(Graphics g) {
        Graphics otherGraphics = image.getGraphics();
        super.paint(otherGraphics);
        snake.draw(otherGraphics);
        egg.draw(otherGraphics);
        g.drawImage(image, 0, 0, null);
    }

    public static void main(String[] args) {
        new SnakeGameFrame().setVisible(true);
    }
}

作业

2.设计电话薄
联系人

package com.kygo.book;
public class Contact {
    private String name;
    private String tel;
    
    public Contact(String name, String tel) {
        this.name = name;
        this.tel = tel;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getTel() {
        return tel;
    }

    public void setTel(String tel) {
        this.tel = tel;
    }
    
    @Override
    public String toString() {
        return "姓名:" + name + "\n电话号码:" + tel;
    }
}

通讯录:

public class AddressBook {
    private List<Contact> list = new ArrayList<>();
    
    public Contact query(String name) {
        for (Contact contact : list) {
            if (contact.getName().equals(name)) {
                return contact;
            }
        }
        return null;
    }   
public List<Contact> queryAll() {
        return list;
    }
    public boolean add(Contact contact) {
        if (list.add(contact)) {
            return true;
        }
        return false;
    }
    
    public boolean remove(String name) {
        Contact contact = query(name);
        if (list.remove(contact)) {
            return true;
        }
        return false;
    }
    
    public boolean update(Contact contact, String name, String tel) {
        if (list.contains(contact)) {
            int index = list.indexOf(contact);
            list.get(index).setName(name);
            list.get(index).setTel(tel);
            return true;
        }
        else {
            return false;
        }
    }
}

测试:

        Scanner input = new Scanner(System.in);
        AddressBook addressBook = new AddressBook();
        boolean goOn = true;
        while (goOn) {
            System.out.println("欢迎使用通讯录: \n请选择你要使用的功能: \n" 
        + "1.查询\n2.添加\n3.修改\n4.删除\n5.查询所有\n6.退出");
            int choose = input.nextInt();
            if (1 <= choose && choose <= 6) {
                switch (choose) {
                case 1:
                {
                    System.out.print("请输入你要查询联系人的名字: ");
                    String name = input.next();
                    System.out.println(addressBook.query(name));
                    break;
                }
                case 2:
                {
                    System.out.print("请输入联系人名称: ");
                    String name = input.next();
                    System.out.print("请输入联系人电话: ");
                    String tel = input.next();
                    Contact contact = new Contact(name, tel);
                    if (addressBook.add(contact)) {
                        System.out.println("添加联系人成功!");
                    }
                    else {
                        System.out.println("添加联系人失败");
                    }
                    break;
                }
                case 3:
                {
                    System.out.print("请输入你要修改的联系人姓名: ");
                    String name = input.next();
                    if (addressBook.query(name) != null) {
                        System.out.print("请输入新名字: ");
                        String newName = input.next();
                        System.out.print("请输入新电话: ");
                        String newTel = input.next();
                        Contact contact = addressBook.query(name);
                        if (addressBook.update(contact, newName, newTel)) {
                            System.out.println("修改联系人成功!");
                        } else {
                            System.out.println("修改联系人失败");
                        } 
                    }
                    else {
                        System.out.println("没有这个联系人!");
                    }
                    break;
                }
                case 4:
                {
                    System.out.print("请输入你要删除联系人的名字: ");
                    String name = input.next();
                    if (addressBook.remove(name)) {
                        System.out.println("删除联系人成功!");
                    }
                    else {
                        System.out.println("删除联系人失败");
                    }
                    break;
                }
                case 5:
                {
                    List<Contact> list = addressBook.queryAll();
                    for (Contact contact : list) {
                        System.out.println(contact);
                    }
                }
                case 6:
                    goOn = false;
                    break;
                }
            }
        }
        input.close();

Java学习笔记 - 第017天

每日要点

容器

容器(集合框架Container) - 承载其他对象的对象

List

杂项

例子

贪吃蛇

作业

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