多选题Which two scenarios are NOT safe to replace a StringBuffer object with a StringBuilder object？（）AWhen using versions of Java technology earlier than 5.0.BWhen sharing a StringBuffer among multiple threads.CWhen using the java.io class StringBufferInput

第1题：

Which two statements are true about the hashCode method？（）

• A、 The hashCode method for a given class can be used to test for object equality and object inequality for that class.
• B、 The hashCode method is used by the java.util.SortedSet collection class to order theelements within that set.
• C、 The hashCode method for a given class can be used to test for object inequality， but NOT object equality， for that class.
• D、 The only important characteristic of the values returned by a hashCode method is that the distribution of values must follow a Gaussian distribution.
• E、 The hashCode method is used by the java.util.HashSet collection class to group the elements within that set into hash buckets for swift retrieval.

第2题：

public class TestString3 {  public static void main（String[] args） {  // insert code here  System.out.println（s）；  }  }  Which two code fragments， inserted independently at line 3， generate the output 4247？（）

• A、 String s = “123456789”； s = （s-”123”）.replace（1，3，”24”） - “89”；
• B、 StringBuffer s = new StringBuffer（”123456789”）； s.delete（0，3）.replace（ 1，3， “24”）.delete（4，6）；
• C、 StringBuffer s = new StringBuffer（”123456789”）； s.substring（3，6）.delete（ 1 ，3）.insert（1， “24”）；
• D、 StringBuilder s = new StringBuilder（”123456789”）； s.substring（3，6）.delete（ 1 ，2）.insert（ 1， “24”）；
• E、 StringBuilder s = new StringBuilder（”123456789”）； s.delete（0，3）.delete（ 1 ，3）.delete（2，5）.insert（ 1， “24”）；

第3题：

第4题：

Which methods from the String and StringBuffer classes modify the object on which they are called？（）  

• A、The charAt（） method of the String class.
• B、The toUpperCase（） method of the String class.
• C、The replace（） method of the String class.
• D、The reverse（） method of the StringBuffer class.
• E、The length（） method of the StringBuffer class.

第5题：

Given this method in a class：  public String toString（） {  StringBuffer buffer = new StringBuffer（）；  buffer.append（‟<‟）；  buffer.append（this.name）；  buffer.append（‟>‟）；  return buffer.toString（）；  }  Which is true？（） 

• A、 This code is NOT thread-safe.
• B、 The programmer can replace StringBuffer with StringBuilder with no other changes.
• C、 This code will perform well and converting the code to use StringBuilder will not enhance the performance.
• D、 This code will perform poorly. For better performance， the code should be rewritten： return “<“+ this.name + “>”；

第6题：

Whichtwo scenarios are NOT safe to replace a StringBuffer object with a StringBuilder object？（）

• A、When using versions of Java technology earlier than 5.0.
• B、When sharing a StringBuffer among multiple threads.
• C、When using the java.io class StringBufferInputStream.
• D、When you plan to reuse the StringBuffer to build more than one string.
• E、Enitiation of separate design processes to the separation of users

第7题：

What two descriptions best define DWDM？ （）

• A、 a WDM system that is compatible with EDFA technology
• B、 an optical technology for transmitting up to 16 channels over multiple fiber strands
• C、 an optical technology for transmitting up to 32 channels over multiple fiber strands
• D、 a technology for transmitting multiple optical signals using less sophisticated transceiver designthen CWDM
• E、 a technology for transmitting more closely packed optical signals using more sophisticatedtransceiver designs than CWDM

第8题：

Dense Wavelength Division Multiplexing (DWDM) is an important innovation in optical networks.Which two descriptions best define DWDM?（）

• A、optical technology for transmitting up to 32 channels over multiple fiber strands
• B、optical technology for transmitting up to 16 channels over multiple fiber strands
• C、a WDM system that is compatible with EDFA technology
• D、a technology for transmitting more closely packed optical signals using more sophisticated transceiver designs than CWDM .

第9题：

public class Team extends java.util.LinkedList {  public void addPlayer（Player p） {  add（p）；  }  public void compete（Team opponent） { /* more code here */ }  }  class Player { /* more code here */ }  Which two are true？（）

• A、 This code will compile.
• B、 This code demonstrates proper design of an is-a relationship.
• C、 This code demonstrates proper design of a has-a relationship.
• D、 A Java programmer using the Team class could remove Player objects from a Team object.

第10题：

Public class test （  Public static void stringReplace （String text）  （  Text = text.replace （‘j’ ， ‘i’）；  ）  public static void bufferReplace （StringBuffer text）  （  text = text.append （“C”）  ）   public static void main （String args[]}  （  String textString = new String （“java”）； StringBuffer text BufferString = new StringBuffer （“java”）；  stringReplace （textString）；  bufferReplace （textBuffer）；  System.out.printLn （textString + textBuffer）；  ） ）  What is the output？（）