1、transient关键字只能修饰变量，而不能修饰方法和类。
2、被transient关键字修饰的变量不再能被序列化，一个静态变量不管是否被transient修饰，均不能被序列化。
3、一旦变量被transient修饰，变量将不再是对象持久化的一部分，该变量内容在序列化后无法获得访问。也可以认为在将持久化的对象反序列化后，被transient修饰的变量将按照普通类成员变量一样被初始化。

package com.design.prompt;

import java.io.Serializable;

public class UserTest implements Serializable {

    /**
     * 
     */
    private static final long serialVersionUID = 6522988290199824802L;
    private String username;
    transient String password;
    
    public String getUsername() {
        return username;
    }
    public void setUsername(String username) {
        this.username = username;
    }
    public String getPassword() {
        return password;
    }
    public void setPassword(String password) {
        this.password = password;
    }
}

package com.design.prompt;

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;

import org.junit.Test;

public class TransientTest {

    @Test
    public void test_transient() {
        UserTest ut = new UserTest();
        ut.setUsername("jane");
        ut.setPassword("123456");

        System.out.println("read before Serializable: ");
        System.out.println("before username: " + ut.getUsername());
        System.err.println("before password: " + ut.getPassword());
        try {
            ObjectOutputStream os = new ObjectOutputStream(
                    new FileOutputStream("C:/user.txt"));
            os.writeObject(ut); // 将User对象写进文件
            os.flush();
            os.close();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
        try {
            ObjectInputStream is = new ObjectInputStream(new FileInputStream(
                    "C:/user.txt"));
            ut = (UserTest) is.readObject(); // 从流中读取User的数据
            is.close();

            System.out.println("\nread after Serializable: ");
            System.out.println("after username: " + ut.getUsername());
            System.err.println("after password: " + ut.getPassword());

        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
    }
}

执行结果：

before password: 123456
read before Serializable: 
before username: jane
after password: null

read after Serializable: 
after username: jane