Java基础——根类与String类

    public static void main(String[] args) {
        Object object = new Object();
        int hashCode = object.hashCode();
        System.out.println(hashCode);       //26171428

        Student s1 = new Student("张三", 23);
        Student s2 = new Student("李四", 24);
        Student s3 = s1;
            
        System.out.println(s1.hashCode());  //6330655
        System.out.println(s2.hashCode());  //31782850
        System.out.println(s3.hashCode());  //6330655  与s1的hashCode值相同
    }

public static void main(String[] args) {
    Student s = new Student("张三", 23);//创建Student对象 s
    //s对象调用getClass()返回一个描述Student类的class文件的对象，也就是Class类的对象
    Class clazz = s.getClass();    
    //clazz对象调用 Class类的getName() 返回一个String类型,类的全路径名
    String name = clazz.getName();
    System.out.println(name);   
    Student s1 = new Student();//新创建了一个s1对象 
    //s1对象调用getClass() 返回一个描述Student类的class文件的对象,也就是Class类的对象
    Class clazz1 = s1.getClass();       
    //因为clazz和clazz1都是描述Student类的class文件的对象 所以他俩是同一个对象
    System.out.println(clazz == clazz1);    
}

public class Student {
    String name;
    int age;
    public Student(String name, int age){
        this.name = name;
        this.age = age;
    }
    @Override
    public String toString() {
        return "Student [name=" + name + ", age=" + age + "]";
    }
}
public static void main(String[] args) {
    Student s = new Student("张三", 23);
    System.out.println(s);      //这句话就相当于 System.out.println(s.toString());
}

public class Student {
   String name;
   int age;
   public Student(String name, int age){
       this.name = name;
       this.age = age;
   }
   //重写equals方法
   //参数必须是Object，因为重写Object的方法，方法体必须和Object的equals方法一模一样
   @Override
   public boolean equals(Object obj) {      
       Student s = (Student)obj;//因为obj不能调用Student特有的内容,所以向下转型
       return this.name.equals(s.name) &&this.age == s.age;                            //this.name.equals(s.name) 这儿的equals方法是String类重写Object后的equals方法
   }
  }
  public static void main(String[] args) {
      Student s1 =  new Student("张三", 23);
      Student s2 =  new Student("张三", 23);
      boolean b = s1.equals(s2);       //比较2个对象属性是否相同
      System.out.println(s1 == s2);    //false 比较的是两个对象的地址值是否相同
      System.out.println(b);            //true
   }

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);        //创建键盘录入对象
        if(sc.hasNextInt()) {               //判断键盘录入的是否是int类型的数据
            int i = sc.nextInt();           //键盘录入的数据存储在i中
            System.out.println(i);
        }else {
            System.out.println("输入的类型错误");
        }
    }

    String s = "abc";  s就是String的一个对象
    public String():空构造
    public String(byte[] bytes):把字节数组转成字符串
    public String(byte[] bytes,int index,int length):把字节数组的一部分转成字符串
    public String(char[] value):把字符数组转成字符串
    public String(char[] value,int index,int count):把字符数组的一部分转成字符串
    public String(String original):把字符串常量值转成字符串

    public static void main(String[] args) {
        String s = "abc";
        System.out.println(s1);        //打印出：abc
        
        String s1 = new String();
        System.out.println(s1);        //s1是个空串
        
        byte[] arr1 = {97,98,99};       
        String s2 = new String(arr1);   //解码,将计算机读的懂的转换成我们读的懂
        System.out.println(s2);        //打印出：abc
        
        byte[] arr2 = {97,98,99,100,101,102};
        String s3 = new String(arr2,2,3);   //将arr2字节数组从2索引开始转换3个
        System.out.println(s3);        //打印出：cde
        
        char[] arr3 = {'a','b','c','d','e'};    //将字符数组转换成字符串
        String s4 = new String(arr3);
        System.out.println(s4);        //打印出：abdcde
        
        String s5 = new String(arr3,1,3);   //将arr3字符数组,从1索引开始转换3个
        System.out.println(s5);        //打印出：bcd
        
        String s6 = new String("heima");
        System.out.println(s6);        //打印出 ：heima
    }