11. 字符串操作优化
在对字符串实行+操作时，最好用一条语句
// Your source code looks like…
String str = “profit = revenue( ” revenue
“ – cost( ” cost ““;
// 编译方法
String str = new StringBuffer( ).append( “profit = revenue( “ ).
append( revenue ).append( “ – cost( “ ).
append( cost ).append( ““ ).toString( );
在循环中对字符串操作时改用StringBuffer.append()方法
String sentence = “”;
for( int i = 0; i < wordArray.length; i++ ) {
sentence += wordArray[ i ];
}
优化为
StringBuffer buffer = new StringBuffer( 500 );
for( int i = 0; i < wordArray.length; i++ ) {
buffer.append( wordArray[ i ] );
}
String sentence = buffer.toString( );
12. 对象重用(特别对于大对象来说)
public
class Point
{
public int x;
public int y;
public Point( )
{
this( 0, 0 );
}
}
优化为：
public class Component
{
private int x;
private int y;
public Point getPosition( )
{
Point rv = new Point( ); // Create a new Point
rv.x = x; // update its state
rv.y = y;
return rv;
}
}
// Process an array of Component positions…
for( int i = 0; i < componentArray.length; i++ ) {
Point position = componentArray[i].getPosition( );
// Process position value…
// Note: A Point object is created for each iteration
// of the loop…
}
可再次优化，仅使用一个类对象：)
public
class Component
{
private int x;
private int y;
public Point getPosition( Point rv )
{
if( rv == null) rv = new Point( );
rv.x = x; // update its state
rv.y = y;
return rv;
}
// Create a single point object and reuse it…
Point p = new Point( );
for( int i = 0; i < componentArray.length; i++ ) {
Point position = componentArray[i].getPosition( p );
// Process position value…
// Note: Only one Point object is ever created.
}
13. J2EE相关
a) 尽量不要将大对象放到HttpSession或其他须序列化的对象中，并注意及时清空Session
b) 使用预编译语句prepareStatement代替createStatement
c) 尽可能使用连接池
d) 能使用Cache就使用Cache，具体实现可参考jive(CacheCacheableCacheObjectCacheSizesDefaultCacheLinkdListLinkdListNode)或ofbiz(org.ofbiz.core.util. UtilCache.Java)
3COME考试频道为您精心整理，希望对您有所帮助，更多信息在http://www.reader8.net/exam/
