JAVA笔记10__Math类、Random类、Arrays类/日期操作类/对象比较器/对象的克隆/二叉树

/**

 * Math类、Random类、Arrays类：具体查JAVA手册。。。。。。

 */

public class Main {

    public static void main(String[] args) {

        String[] s1 = {"a","b","c","d","e"};

        String[] s2 = {"a","b","c","d","e"};

        boolean b = Arrays.equals(s1,s2); //比较两数组内容

        System.out.println(b); //输出true

        String[] s3 = new String[6];

        Arrays.fill(s3,"井空");

        System.out.println(s3.length);

        for(String i:s3) System.out.print(i+" "); System.out.println();

        String[] s4 = Arrays.copyOfRange(s1, 2, 3); //[2,3)

        for(String i:s4) System.out.print(i+" "); System.out.println();

        int index = Arrays.binarySearch(s1, "c");

        System.out.println(index);

    }

}

/**

 * 日期操作类

 * Date类：表示特定的瞬间，精确到毫秒，也是程序运行时的当前时间

 * Calendar类：可以精确到毫秒

 * DateFormat类

 * SimpleDateFormat类：日期格式化类

 */

public class Main {

    public static void main(String[] args) {

        Date d1 = new Date();

        Date c = new Date();

        System.out.println(d1.getTime()); //毫秒表示

        System.out.println(d1); //格式表示

        //两种实例化方式

        Calendar ca1 = Calendar.getInstance();

        Calendar ca2 = new GregorianCalendar(); //阳历

        int year = ca1.get(Calendar.YEAR);

        int month = ca1.get(Calendar.MONTH)+1;

        int day = ca1.get(Calendar.DAY_OF_MONTH);

        int hour = ca1.get(Calendar.HOUR);

        int minute = ca1.get(Calendar.MINUTE);

        int second = ca1.get(Calendar.SECOND);

        System.out.println(year+" "+month+" "+day);

        System.out.println(hour+" "+minute+" "+second);

        DateFormat df1 = DateFormat.getDateInstance();

        DateFormat df2 = DateFormat.getTimeInstance();

        String nowDate = df1.format(new Date());

        String nowTime = df2.format(new Date());

        System.out.println(nowDate);

        System.out.println(nowTime);

        SimpleDateFormat sdf1 = new SimpleDateFormat("yyyy^MM^dd HH:mm:ss SSS毫秒");

        String swa = sdf1.format(new Date());

        System.out.println(swa);

    }

}

/**

 * 对象比较器：对两个或多个数据项进行比较，以确定它们是否相等，或确定它们之间的大小关系

 * Comparable接口：强行对实现它的每个类的对象进行整体排序，类的compareTo方法被称为它的自然比较方法

 * 如果自定义类的对象要实现排序，那么就要实现Comparable接口，并实现接口的CompareTo方法

 *

 * Comparable接口要求自定义类去实现，按照OO原则：对修改关闭，对扩展开放。

 * 如果这个类已经定义好，不想再去修改它，如何实现？ 答：Arrays.sort有一个重载方法：

 */

public class Main {

    public static void main(String[] args) {

        String[] names = {"a","b","c","d","e","f"};

        Person[] persons = {

            new Person("a",10), new Person("b",9),

            new Person("c",8),  new Person("d",7),

            new Person("e",6),  new Person("f",5),

        };

        //自定义类对对象数组排序

        Arrays.sort(persons);

        for(Person i:persons) System.out.println(i.name+" "+i.age);

        Person2[] persons2 = {

            new Person2("a",10), new Person2("b",9),

            new Person2("c",8),  new Person2("d",7),

            new Person2("e",6),  new Person2("f",5),

        };

        Arrays.sort(persons2,new Person2Comparator()); //使用自定义的比较器

        for(Person2 i:persons2) System.out.println(i.name+" "+i.age);

        System.out.println(Arrays.toString(persons2));//返回数组内容的字符串表示形式

    }

}

class Person implements Comparable<Person>{

    public String name;

    public int age;

    Person(String name,int age){

        this.name = name;

        this.age = age;

    }

    @Override

    public int compareTo(Person o) { //比较器的比较方法

        //实现：定义对象之间的比较规则

        if(o==null){

            throw new NullPointerException();

        }

        //如果当前对象小于参数对象，返回-1

        //如果当前对象等于参数对象，返回0

        //如果当前对象大于参数对象，返回1

        if(this.age < o.age)

            return -1;

        else if(this.age < o.age)

            return 1;

        return 0;

    }

}

class Person2{

    public String name;

    public int age;

    Person2(String name,int age){

        this.name = name;

        this.age = age;

    }

}

class Person2Comparator implements Comparator<Person2>{

    @Override

    public int compare(Person2 o1, Person2 o2) {

       if(o1==null || o2==null)

           throw new NullPointerException();

       if(o1.age < o2.age)

           return -1;

       else if(o1.age > o2.age)

           return 1;

       return 0;

    }

}

/**

 * 对象的克隆：将一个对象复制一份（克隆要比new效率高）

 * 一个类要想实现克隆功能，必须：

 * 1.实现Cloneable接口，该接口必须是一个标记接口

 * 2.重写Obejct类中的Clone方法

 */

public class Main {

    public static void main(String[] args) {

        Cat c1 = new Cat("a",10);

        System.out.println("c1="+c1);

        try{

            Cat c2 = (Cat)c1.clone();

            System.out.println("c2="+c2);

        }catch(CloneNotSupportedException e){

            e.printStackTrace();

        }

    }

}

class Cat implements Cloneable{

    private String name;

    private int age;

    public Cat(String name, int age) {

        this.name = name;

        this.age = age;

    }

    public String getName() {

        return name;

    }

    public void setName(String name) {

        this.name = name;

    }

    public int getAge() {

        return age;

    }

    public void setAge(int age) {

        this.age = age;

    }

    @Override

    public String toString() {

        return "Cat{" + "name=" + name + ", age=" + age + '}';

    }

    @Override

    //重写Obejct的Clone方法

    protected Object clone() throws CloneNotSupportedException {

        return super.clone();

    }

}

/**

 * 二叉树

 */

public class Main {

    public static void main(String[] args) {

        BinaryTree t1 = new BinaryTree();

        t1.add(8);

        t1.add(9);

        t1.add(3);

        t1.add(4);

        t1.print();

    }

}

class BinaryTree{

    private Node root;

    public void add(int data){

        if(root==null){

            root = new Node(data);

        }else{

            root.addNode(data);

        }

    }

    public void print(){

        if(root!=null){

            root.printNode();

        }else{

            System.out.println("NULL");

        }

    }

    class Node{

        private int data;

        private Node left;

        private Node right;

        public Node(int data){

            this.data = data;

        }

        public void addNode(int data){

            if(data <= this.data){

                if(this.left==null){

                    this.left = new Node(data);

                }else{

                    this.left.addNode(data);

                }

            }else{

                if(this.right==null){

                    this.right = new Node(data);

                }else{

                    this.right.addNode(data);

                }

            }

        }

        public void printNode(){

            System.out.println(this.data);

            if(this.left!=null)

                this.left.printNode();

            if(this.right!=null)

                this.right.printNode();

        }

    }

}

巴特西

JAVA笔记10__Math类、Random类、Arrays类/日期操作类/对象比较器/对象的克隆/二叉树

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