corejava第10版

corejava第10版/v2ch02/randomAccess/RandomAccessTest.java

@@ -0,0 +1,80 @@
+package randomAccess;
+
+import java.io.*;
+import java.util.*;
+import java.time.*;
+
+/**
+ * @version 1.13 2016-07-11
+ * @author Cay Horstmann
+ */
+public class RandomAccessTest
+{  
+   public static void main(String[] args) throws IOException
+   {
+      Employee[] staff = new Employee[3];
+
+      staff[0] = new Employee("Carl Cracker", 75000, 1987, 12, 15);
+      staff[1] = new Employee("Harry Hacker", 50000, 1989, 10, 1);
+      staff[2] = new Employee("Tony Tester", 40000, 1990, 3, 15);
+
+      try (DataOutputStream out = new DataOutputStream(new FileOutputStream("employee.dat")))
+      {  
+         // save all employee records to the file employee.dat
+         for (Employee e : staff)
+            writeData(out, e);
+      }
+         
+      try (RandomAccessFile in = new RandomAccessFile("employee.dat", "r"))
+      {
+         // retrieve all records into a new array
+            
+         // compute the array size
+         int n = (int)(in.length() / Employee.RECORD_SIZE);
+         Employee[] newStaff = new Employee[n];
+
+         // read employees in reverse order
+         for (int i = n - 1; i >= 0; i--)
+         {  
+            newStaff[i] = new Employee();
+            in.seek(i * Employee.RECORD_SIZE);
+            newStaff[i] = readData(in);
+         }
+         
+         // print the newly read employee records
+         for (Employee e : newStaff) 
+            System.out.println(e);
+      }
+   }
+
+   /**
+    * Writes employee data to a data output
+    * @param out the data output
+    * @param e the employee
+    */
+   public static void writeData(DataOutput out, Employee e) throws IOException
+   {
+      DataIO.writeFixedString(e.getName(), Employee.NAME_SIZE, out);
+      out.writeDouble(e.getSalary());
+
+      LocalDate hireDay = e.getHireDay();
+      out.writeInt(hireDay.getYear());
+      out.writeInt(hireDay.getMonthValue());
+      out.writeInt(hireDay.getDayOfMonth());
+   }
+
+   /**
+    * Reads employee data from a data input
+    * @param in the data input
+    * @return the employee
+    */
+   public static Employee readData(DataInput in) throws IOException
+   {      
+      String name = DataIO.readFixedString(Employee.NAME_SIZE, in);
+      double salary = in.readDouble();
+      int y = in.readInt();
+      int m = in.readInt();
+      int d = in.readInt();
+      return new Employee(name, salary, y, m - 1, d);
+   }  
+}