String、StringBuffer、StringBuilder

public final class String extends Objectimplements Serializable, 
Comparable<String>, CharSequence

public final class StringBuffer extends Objectimplements Serializable, CharSequence

public final class StringBuilder extends Objectimplements Serializable, CharSequence

小小总结：
String拼接时会产生新对象；

StringBuffer拼接时不会产生新对象，多次拼接会比String效率高，而且是线程安全；

StringBuilder的效率又比StringBuffer更高，但不是线程安全，不保证同步；

public class MyString
{
	public static void main(String[] args)
	{
		long t1;
		long t2;
		
		t1 = System.currentTimeMillis();
		String s = "hello ";
		for (int i = 0; i < 1000; i++)
		{
			s += "hello ";
		}
		t2 = System.currentTimeMillis();
		System.out.println(t2 - t1);

		t1 = System.currentTimeMillis();
		StringBuffer sb = new StringBuffer();
		for (int i = 0; i < 1000; i++)
		{
			sb.append("hello ");
		}
		t2 = System.currentTimeMillis();
		System.out.println(t2 - t1);
	}
}