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 Stirng toString() {
   return  getClass().getName() + "@" + Integer.toHexString(hashCode())
}

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 boolean equals(Object obj){
   return (this == obj);
}

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
   }