Java Field hashCode()方法及实例

java.lang.reflect.Field 的 hashCode() 方法用于获取该Field的哈希码。最终的哈希码是作为底层字段的声明类名称和它的名称的哈希码的排他性或计算出来的。如果对象没有变化，哈希码总是相同的。Hashcode是JVM在创建对象时生成的唯一代码。它可以用来对散列相关的算法进行一些操作，如hashtable、hashmap等。一个对象也可以用这个唯一的代码进行搜索。

语法

public int hashCode()

参数： 此方法不接受任何东西。

返回值： 该方法返回一个 整数 ，即该对象的哈希代码值。

以下程序说明了hashCode()方法：

程序1 :

// Java program to demonstrate hashCode() method
  
import java.lang.reflect.Field;
  
public class GFG {
  
    public static void main(String[] args)
        throws Exception
    {
  
        // Get the marks field object
        Field field = User.class.getField("Marks");
  
        // Apply hashCode Method on User Object
        // to get the hashCode of Marks field
        int value = field.hashCode();
  
        // print result
        System.out.println("HashCode of Marks field"
                           + " is " + value);
  
        // Now Get the Fees field object
        field = User.class.getField("Fees");
  
        // Apply hashCode Method on User Object
        // to get the hashcode of Fees field
        value = field.hashCode();
  
        // print result
        System.out.println("HashCode of Fees field"
                           + " is " + value);
  
        // Now Get the name field object
        field = User.class.getField("name");
  
        // Apply hashCode Method on User Object
        // to get the hashCode of name field
        value = field.hashCode();
  
        // print result
        System.out.println("HashCode of name field"
                           + " is " + value);
    }
}
  
// sample User class
class User {
  
    // static double values
    public static double Marks = 34.13;
    public static float Fees = 3413.99f;
    public static String name = "Aman";
  
    public static double getMarks()
    {
        return Marks;
    }
  
    public static void setMarks(double marks)
    {
        Marks = marks;
    }
  
    public static float getFees()
    {
        return Fees;
    }
  
    public static void setFees(float fees)
    {
        Fees = fees;
    }
  
    public static String getName()
    {
        return name;
    }
  
    public static void setName(String name)
    {
        User.name = name;
    }
}

输出:

HashCode of Marks field is 71482573
HashCode of Fees field is 591398
HashCode of name field is 1779040

程序2

// Java program to demonstrate hashCode() method
  
import java.lang.reflect.Field;
import java.time.Month;
  
public class GFG {
  
    public static void main(String[] args)
        throws Exception
    {
  
        // Get all field objects of Month class
        Field[] fields = Month.class.getFields();
  
        for (int i = 0; i < fields.length; i++) {
  
            // print name of Fields
            System.out.println("HashCode of Field: "
                               + fields[i].hashCode());
        }
    }
}

输出:

HashCode of Field: -297508095
HashCode of Field: 1296412905
HashCode of Field: 1475695976
HashCode of Field: 1343692077
HashCode of Field: 1404020238
HashCode of Field: 1401709321
HashCode of Field: 1401709395
HashCode of Field: 538235208
HashCode of Field: 2125827066
HashCode of Field: -1718938229
HashCode of Field: -1007182215
HashCode of Field: 59532142

参考文献 ： https://docs.oracle.com/javase/8/docs/api/java/lang/reflect/Field.html#hashCode-