[Java] 编程思想 - 字符串
plhDigital nomadJava字符串的拼接
下面是一段java字符串拼接代码
public class Conversation {
public static String implicit(String[] fields) {
String result = "";
for(int i = 0; i < fields.length; i++) {
result += fields[i];
}
return result;
}
public String explicit(String[] fields) {
StringBuilder result = new StringBuilder();
for(int i = 0; i < fields.length; i++) {
result.append(fields[i]);
}
return result.toString();
}
public static void main(String[] args) {
String mango = "mango";
String s = "abc" + mango + "def" + 47;
System.out.println(s);
String res = implicit(new String[]{"a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m", "n", "o", "p", "q", "r", "s", "t", "u", "v", "w", "x", "y", "z"});
System.out.println(res);
}
}可以通过javap -c拿到java机器代码,可以看到,下面的代码,java拼接就是单纯拼接,并没用到stringBuilder, 而用java stringBuilder来拼接代码,可以看到全文只生成一个stringBuilder.
Compiled from "Conversation.java"
public class Conversation {
public Conversation();
Code:
0: aload_0
1: invokespecial #1 // Method java/lang/Object."<init>":()V
4: return
public static java.lang.String implicit(java.lang.String[]);
Code:
0: ldc #7 // String
2: astore_1
3: iconst_0
4: istore_2
5: iload_2
6: aload_0
7: arraylength
8: if_icmpge 27
11: aload_1
12: aload_0
13: iload_2
14: aaload
15: invokedynamic #9, 0 // InvokeDynamic #0:makeConcatWithConstants:(Ljava/lang/String;Ljava/lang/String;)Ljava/lang/String;
20: astore_1
21: iinc 2, 1
24: goto 5
27: aload_1
28: areturn
public java.lang.String explicit(java.lang.String[]);
Code:
0: new #13 // class java/lang/StringBuilder
3: dup
4: invokespecial #15 // Method java/lang/StringBuilder."<init>":()V
7: astore_2
8: iconst_0
9: istore_3
10: iload_3
11: aload_1
12: arraylength
13: if_icmpge 30
16: aload_2
17: aload_1
18: iload_3
19: aaload
20: invokevirtual #16 // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
23: pop
24: iinc 3, 1
27: goto 10
30: aload_2
31: invokevirtual #20 // Method java/lang/StringBuilder.toString:()Ljava/lang/String;
34: areturn
public static void main(java.lang.String[]);
Code:
0: ldc #24 // String mango
2: astore_1
3: aload_1
4: invokedynamic #26, 0 // InvokeDynamic #1:makeConcatWithConstants:(Ljava/lang/String;)Ljava/lang/String;
9: astore_2
10: getstatic #29 // Field java/lang/System.out:Ljava/io/PrintStream;
13: aload_2
14: invokevirtual #35 // Method java/io/PrintStream.println:(Ljava/lang/String;)V
17: iconst_3
18: anewarray #41 // class java/lang/String
21: dup
22: iconst_0
23: ldc #43 // String a
25: aastore
26: dup
27: iconst_1
28: ldc #45 // String b
30: aastore
31: dup
32: iconst_2
33: ldc #47 // String c
35: aastore
36: invokestatic #49 // Method implicit:([Ljava/lang/String;)Ljava/lang/String;
39: astore_3
40: getstatic #29 // Field java/lang/System.out:Ljava/io/PrintStream;
43: aload_3
44: invokevirtual #35 // Method java/io/PrintStream.println:(Ljava/lang/String;)V
47: return
}格式化符号
public class Receipt {
private double total = 0;
private Formatter f = new Formatter(System.out);
public void printTitle() {
f.format("%-15s %5s %10s\n", "Item", "Qty", "Price");
f.format("%-15s %5s %10s\n", "----", "---", "-----");
}
public void print(String name, int qty, double price) {
f.format("%-15.15s %5d %10.2f\n",
name, qty, price);
total += price;
}
public void printTotal() {
f.format("%-15s %5s %10.2f\n", "Tax", "", total * 0.06);
f.format("%-15s %5s %10s\n", "", "", "-----");
f.format("%-15s %5s %10.2f\n", "Total", "", total * 1.06);
}
public static void main(String[] args) {
Receipt receipt = new Receipt();
receipt.printTitle();
receipt.print("Jack's Magic Beans", 4, 4.25);
receipt.print("Princess Peas", 3, 5.1);
receipt.print("Three Bears Porridge", 1, 14.29);
receipt.printTotal();
}
}输出如下
Item Qty Price
---- --- -----
Jack's Magic Be 4 4.25
Princess Peas 3 5.10
Three Bears Por 1 14.29
Tax 1.42
-----
Total 25.06字符串正则
public class Splitting {
public static String knights = "Then, when you have found the shrubbery, you must " +
"cut down the mightiest tree in the forest... " +
"with... a herring!";
public static void split(String regex) {
System.out.println(Arrays.toString(knights.split(regex)));
}
public static void main(String[] args) {
split(" ");
split("\\W+");
split("n\\W+");
}
}[Then,, when, you, have, found, the, shrubbery,, you, must, cut, down, the, mightiest, tree, in, the, forest..., with..., a, herring!]
[Then, when, you, have, found, the, shrubbery, you, must, cut, down, the, mightiest, tree, in, the, forest, with, a, herring]
[The, whe, you have found the shrubbery, you must cut dow, the mightiest tree i, the forest... with... a herring!]