小明思考

---Question---

1.What is the output of the following program? 

public class Foo {

       public static void main(String[] args){

              Map<byte[], String> m = new HashMap<byte[], String>();

              byte[] key = "abcd".getBytes();

              m.put(key, "abcd");

              System.out.println(m.containsKey(key));

              System.out.println(m.containsKey("abcd"));

              System.out.println(m.containsKey("abcd".getBytes()));

       }

}

a) true,true,false b)true,false,false c)true,true,true d) false,false,false e)Program throws an exception

2. What is the proper string filled in the following program?

Public class Foo {

       public static void main(String[] args) {

              String s=”1\\2\\3\\4”;

              //split the string with “\”

              String []result = s.split(“____”);

              for(String r:result){

                     System.out.println(r);

              }

       }

}

a) \ b) \\ c) \\\ d)\\\\ e)\\\\\

3. What is the output of the following program? 

public class Foo {

       public static void main(String[] args) {

              char[] c = new char[] { '1' };

              String s = new String(c);

              System.out.println("abcd" + c);

              System.out.println("abcd" + s);

       }

}

a) Compile error b)abcd1,abcd1 c) abcd49,abcd1 d) Program throws an exception e)none of above

4. Which class is threading safe which one object can be used between multi-threads without extra synchronized? 

a) Vector b) HashMap c) ArrayList d)StringBuilder e)HashSet

5. What is the output of the following program? 

public class Foo {

       public static void main(String[] args) throws IOException {

              ByteArrayOutputStream baos = new ByteArrayOutputStream();

              byte[] b = new byte[]{(byte)0x0,(byte)0x1,(byte)0x2};

              baos.write(b);

              baos.write(0x0102);

              byte[] result = baos.toByteArray();

              ByteArrayInputStream bais = new ByteArrayInputStream(result);

              System.out.println(bais.available());

       }

}

a) 0 b) 1 c)4 d) 5 e) Program throws an exception

6. What is return value of function “calc”?

public class Foo {

       public static int calc() throws IOException{

              int ret = 0;

              try{

                     ++ret;

                     throw new IOException("try");

              }

              catch(IOException ioe){

                     --ret;

                     return ret;

              }

              finally{

                     ++ret;

                     return ret;

              }

       }

}

a) 0 b) 1 c)2 d)3 e) throws an exception

7. What is the output of the following program?

public class Foo {

       public static class Value {

              private int value;

              public int get(){

                     return value;

              }

              public void set(int v){

                     value = v;

              }

       }

       public static class Values implements Iterable<Value>{

              public Values(int capacity){

                     this.capacity = capacity;

              }

              int count =1 ;

              int capacity;

              Value v = new Value();

              public Iterator<Value> iterator() {

                     return new Iterator<Value>(){

                            public boolean hasNext() {

                                   return count<=capacity;

                            }

                            public Value next() {

                                   v.set(count++);

                                   return v;

                            }

                            public void remove() {

                                   throw new UnsupportedOperationException();

                            }

                     };

              }

       }

       public static void main(String[] args) {

              Values vs = new Values(10);

              Value result = null;

              for(Value v:vs){

                     if(result ==  null){

                            result = v;

                     }

                     else{

                            result.set(result.get()+v.get());

                     }

              }

              System.out.println(result.get());

       }

}

a)       20 b)40 c)45 d)55 e)throws NullpointerException

8. If add keyword “final” before a class member function, it means:

a) The method can’t access the non-final member variable.

b) The method can’t modify the member variable.

c) The method can’t be override by subclass.

d) The method is a thread-safe function.

e) The method can’t be accessed by other non-final function.

9. About java memory and garbage collector, which statement is correct?

a) Moving variable from locale to class will make GC more effectively.

b) When Full GC is executing, all the user threads will be paused.

c) If object A contains a reference of object B and object B contains a reference of object A, the two objects can’t be reclaimed by GC.

d) When a thread exits, all objects which created by that thread will be reclaimed

e) It is recommended that calling “System.gc()” to control the memory usage.

10. About java classpath and classloader, which statement is NOT correct?

a) User can specify the classpath by using the option “-cp” in Java command line.

b) If user doesn’t specify classpath, the JVM search the class from the current folder by default.

c) A JVM can load two different versions of a library.

d) To define customized class loader, it is possible to load class from internet at runtime.

11. Which data structure has best performance when remove an element from it?

a) Vector b)ArrayList c)LinkedList d)HashMap e)HashSet

12. Which is the correct way to convert bytes from charset “gb2312” to “utf-8”?

byte[] src , dst;

a) dst = new String(src,”utf-8”).getBytes(“gb2312”);

b) dst = new String(src,”gb2312”).getBytes(“utf-8”);

c) dst = new String(src,”utf-16”).getBytes();

d) dst = new String(src).getBytes();

e) None of above.

Here is my some recommendations for java i18n .

1.  The correct way to handle text-based resource files for localization

 Use java.util.ResourceBoundle to read resource from file.

e.g.
 Local local = Local.CHINA;
 ResourceBundle rb = ResourceBundle.getBundle("test", local);
 String title = rb.getString("helloworld.title");
 System.out.println(title);

 //The program will read file: test_zh.properties
 # This locale is zh_CN
 # helloworld.title=中文1234
 and the file should use native2ascii program to convert (native2ascii.exe is in JDK)
 # This locale is zh_CN
 helloworld.title=\u4f60\u597d1234

 if you don't use native2ascii  to covert,you must covert it in the java program,like this:
 ResourceBundle rb = ResourceBundle.getBundle("test", Locale.CHINA);
     String title = rb.getString("helloworld.title");
    System.out.println(new String(title.getBytes("8859_1")));  //covert to os/jvm default charset

2.       Locale driven date and time display
 
 Use java.text.DateFormat to format date string
e.g.
 DateFormat df = DateFormat.getDateInstance(DateFormat.FULL,Locale.CHINA);
 String date = df.format(new Date());
    System.out.println(date);

 DateFormat df2 = DateFormat.getDateTimeInstance(DateFormat.DEFAULT,DateFormat.DEFAULT,Locale.CHINA);
 String datetime = df2.format(new Date());
    System.out.println(datetime);

3.       JSP localization method.

1) native method:
 use "Local local = request.getLocale();" to get the page accessor's local info
 then use ResourceBoundle to read local resource
 and page should use utf-8 charset
 
e.g.
<%@ page contentType="text/html; charset=utf-8" %>
<%
Local local = request.getLocale();
ResourceBundle rb = ResourceBundle.getBundle("test", local);
String title = rb.getString("helloworld.title");
%>
<html>
<head>
<title>test</title>
</head>
<body bgcolor="#ffffff">
<h1><%=title%></h1>
</body>
</html>
notice:put the  test_zh.properties into directionary WEB_INF/classes

2)use jsp taglib to simplify the page

 the Jakarta i18n taglib is a good choice. http://jakarta.apache.org/taglibs/doc/i18n-doc/index.html
e.g.
<%@ page contentType="text/html; charset=utf-8"%>
<%@ taglib uri="http://jakarta.apache.org/taglibs/i18n-1.0" prefix="i18n" %>
<i18n:bundle baseName="test" id="test" localeRef="userLocale"
             scope="request"
             changeResponseLocale="false"/>
<html>
<head>
<title>test</title>
</head>
<body bgcolor="#ffffff">
<h1><i18n:message key="helloworld.title" /></h1>
</body>
</html>

3）use j2ee web framework(Struts) to simplify

 the Struts web framework supply i18n support
 Please refer: http://www.allapplabs.com/struts/struts_internationalization.htm