1.strictfp, 即 strict float point (精確浮點)。
strictfp 關鍵字可應用於類、接口或方法。使用 strictfp 關鍵字聲明一個方法時，該方法中所有的float和double表達式都嚴格遵守FP-strict的限制,符合IEEE-754規範。當對一個類或接口使用 strictfp 關鍵字時，該類中的所有代碼，包括嵌套類型中的初始設定值和代碼，都將嚴格地進行計算。嚴格約束意味着所有表達式的結果都必須是 IEEE 754 算法對操作數預期的結果，以單精度和雙精度格式表示。
如果你想讓你的浮點運算更加精確，而且不會因爲不同的硬件平臺所執行的結果不一致的話，可以用關鍵字strictfp.
示例 1
下面的示例演示了一個使用 strictfp 修飾符聲明的類。
Java代碼
package com.magical;
// Example of precision control with strictfp
public strictfp class MyClass {
public static void main(String[] args)
{
float aFloat = 0.6710339f;
double aDouble = 0.04150553411984792d;
double sum = aFloat + aDouble;
float quotient = (float)(aFloat / aDouble);
System.out.println("float: " + aFloat);
System.out.println("double: " + aDouble);
System.out.println("sum: " + sum);
System.out.println("quotient: " + quotient);
}
}
package com.magical;
// Example of precision control with strictfp
public strictfp class MyClass {
public static void main(String[] args)
{
float aFloat = 0.6710339f;
double aDouble = 0.04150553411984792d;
double sum = aFloat + aDouble;
float quotient = (float)(aFloat / aDouble);
System.out.println("float: " + aFloat);
System.out.println("double: " + aDouble);
System.out.println("sum: " + sum);
System.out.println("quotient: " + quotient);
}
}
運行結果：
float: 0.6710339
double: 0.04150553411984792
sum: 0.7125394529774224
quotient: 16.167336
2.transient
當串行化某個對象時，如果該對象的某個變量是transient，那麼這個變量不會被串行化進去。也就是說，假設某個類的成員變量是transient，那麼當通過
ObjectOutputStream把這個類的某個實例
保存到磁盤上時，實際上transient變量的值是不會保存的。因爲當從磁盤中讀出這個對象的時候，對象的該變量會沒有被賦值。
另外這篇文章還提到，當從磁盤中讀出某個類的實例時，實際上並不會執行這個類的構造函數，而是讀取這個類的實例的狀態，並且把這個狀態付給這個類的對象。
import java.util.*;
public class LoggingInfo implements java.io.Serializable
{
private Date loggingDate = new Date();
private String uid;
private transient String pwd;
LoggingInfo(String user, String password)
{
uid = user;
pwd = password;
}
public String toString()
{
String password=null;
if(pwd == null)
{
password = "NOT SET";
}
else
{
password = pwd;
}
return "logon info: \n " + "user: " + uid +
"\n logging date : " + loggingDate.toString() +
"\n password: " + password;
}
}
import java.io.*;
public class Serializable{
public static void main(String args[]){
LoggingInfo logInfo = new LoggingInfo("小徐", "不知道");
System.out.println(logInfo.toString());
try
{
ObjectOutputStream o = new ObjectOutputStream(
new FileOutputStream("logInfo.out"));
o.writeObject(logInfo);
o.close();
}
catch(Exception e) {//deal with exception
e.printStackTrace();
}
// To read the object back, we can write
try
{
ObjectInputStream in =new ObjectInputStream(
new FileInputStream("logInfo.out"));
LoggingInfo logInfo1 = (LoggingInfo)in.readObject();
System.out.println(logInfo1.toString());
}
catch(Exception e)
{//deal with exception
e.printStackTrace();
}
}
}
import java.util.*;
public class LoggingInfo_ implements java.io.Serializable
{
private Date loggingDate = new Date();
private String uid;
private transient String pwd;
public LoggingInfo_()
{
this.uid = "小徐";
this.pwd = "不知道";
}
public String toString()
{
String password=null;
if(pwd == null)
{
password = "NOT SET";
}
else
{
password = pwd;
}
return "logon info: \n " + "user: " + uid +
"\n logging date : " + loggingDate.toString() +
"\n password: " + password;
}
}
import java.io.*;
public class Serializable_{
public static void main(String args[]){
LoggingInfo_ logInfo_ = new LoggingInfo_();
System.out.println(logInfo_.toString());
try
{
ObjectOutputStream o = new ObjectOutputStream(
new FileOutputStream("logInfo_.out"));
o.writeObject(logInfo_);
o.close();
}
catch(Exception e) {//deal with exception
e.printStackTrace();
}
// To read the object back, we can write
try
{
ObjectInputStream in =new ObjectInputStream(
new FileInputStream("logInfo_.out"));
LoggingInfo_ logInfo_1 = (LoggingInfo_)in.readObject();
System.out.println(logInfo_1.toString());
}
catch(Exception e)
{//deal with exception
e.printStackTrace();
}
}
}