第13章 字串

1、String物件預設為不可變的，因此任何貌似對String的改變本質都是建立一個新的String物件，並返回它的引用。

2、在構建String物件時，由於不斷地產生中間的String物件，這樣效率極低，因此建議使用StringBuider物件。

//: strings/UsingStringBulider.java
import java.util.*;

public class UsingStringBulider{
	public static Random rand = new Random(47);
	public String toString(){
		StringBuilder result = new StringBuilder("[");
		for(int i=0; i<25; i++){
			result.append(rand.nextInt(100));
			result.append(", ");
		}
		result.delete(result.length()-2, result.length());
		result.append("]");
		return result.toString();
	}
	public static void main(String[] args){
		UsingStringBulider usb = new UsingStringBulider();
		System.out.println(usb);
	}
}/*Output
[58, 55, 93, 61, 61, 29, 68, 0, 22, 7, 88, 28, 51, 89, 9, 78, 98, 61, 20, 58, 16, 40, 11, 22, 4]
*///:~
 

3、格式化輸出

System.out.format("Row 1: [%d %f]\n", x, y);
System.out.printf("Row 1: [%d %f]\n", x, y);
String str = String.format("Row 1: [%d %f]\n", x, y);

特殊格式實現

4、正則表示式

import static java.lang.System.out; 
// out is a method, but it returns a class which has a println method
import java.util.*;
import java.util.regex.*;


public class IntegerMatch{
	public static void main(String[] args){
		// begin with a capital letter and end with a period
		out.println("This is a test.".matches("^[A-Z].*\\.$"));
		// split with the and you
		out.println(Arrays.toString("This is the goal, you must do better.".split("the|you")));
		// replace all vowels with underline
		out.println("This is the goal, you must do better.".replaceAll("[aeiou]","_"));
		String s = "Java now has regular expressions";
		String regex = "n.w\\s+h(a|i)s";
		Pattern p = Pattern.compile(regex);
		Matcher m = p.matcher(s);
		while(m.find())
			out.println("Match \"" + m.group() + "\" at positions " + m.start() + "-" + (m.end() - 1));
		
		String str = "Arline ate eight apples and one orange while Anita hadn't any";
		String regex2 = "(?i)((^[aeiou])|(\\s+[aeiou]))\\w+?[aeiou]\\b"; // (?i): Case insensitivity
		Pattern p2 = Pattern.compile(regex2);
		Matcher m2 = p2.matcher(str);
		while(m2.find())
			out.println("Match \"" + m2.group() + "\" at positions " + m2.start() + "-" + (m2.end() - 1));
	}
}/* Output
true
[This is ,  goal, ,  must do better.]
Th_s _s th_ g__l, y__ m_st d_ b_tt_r.
Match "now has" at positions 5-11
Match "Arline" at positions 0-5
Match " ate" at positions 6-9
Match " one" at positions 27-30
Match " orange" at positions 31-37
Match " Anita" at positions 44-49
*///:~