Muligvis er den oprindelige spørgsmåls-stiller mere forvirret
end godt er over den lidt mudrede debat.
Jeg har lige prøvet at lavet et eksempel som indeholder alle de
forskellige metoder i en form der skulle være korrekt:
public class ReplaceTest {
private final static int N = 10000;
public static void main(String[] args) {
test(new ReplaceRecursiveString());
test(new ReplaceSmartRecursiveString());
test(new ReplaceRecursiveStringBuffer());
test(new ReplaceRecursiveGlobalStringBuffer());
test(new ReplaceLoopString());
test(new ReplaceLoopStringBuffer());
return;
}
private static void test(Replacer r) {
verify(r);
perf(r);
return;
}
private static void verify(Replacer r) {
if (!r.replaceAll("123<P>456<P>789", "<P>", "\n").equals("123\n456\n789")
|| !r.replaceAll("<P>123<P>456<P>789<P>", "<P>", "\n").equals("\n123\n456\n789\n")
|| !r.replaceAll("123<P><P>456", "<P>", "\n").equals("123\n\n456")
|| !r.replaceAll("<P>", "<P>", "\n").equals("\n")
|| !r.replaceAll("", "<P>", "\n").equals("")) {
System.out.println(r.getMethod() + " failed");
}
return;
}
private static void perf(Replacer r) {
System.out.println(r.getMethod() + ":");
perf("short text - few replaces", r, 1000, 5);
perf("short text - many replaces", r, 1000, 25);
perf("long text - few replaces", r, 10000, 5);
perf("long text - many replaces", r, 10000, 25);
return;
}
private static void perf(String title, Replacer r, int txtlen, int nrepl) {
StringBuffer sb = new StringBuffer("");
for (int i = 0; i < txtlen; i++) {
sb.append('A');
if ((i % (txtlen / nrepl)) == 0) {
sb.append("<P>");
}
}
perf(title, r, sb.toString());
return;
}
private static void perf(String title, Replacer r, String s) {
long t1 = System.currentTimeMillis();
for (int i = 0; i < N; i++) {
r.replaceAll(s, "<P>", "\n");
}
long t2 = System.currentTimeMillis();
System.out.println(title + " = " + (t2 - t1));
return;
}
}
interface Replacer {
public String getMethod();
public String replaceAll(String s, String s1, String s2);
}
class ReplaceRecursiveString implements Replacer {
public String getMethod() {
return "Recursive with String";
}
public String replaceAll(String s, String s1, String s2) {
int ix = s.indexOf(s1);
if (ix >= 0) {
return replaceAll(s.substring(0, ix) + s2 + s.substring(ix + s1.length()), s1, s2);
} else {
return s;
}
}
}
class ReplaceSmartRecursiveString implements Replacer {
public String getMethod() {
return "Smart recursive with String";
}
public String replaceAll(String s, String s1, String s2) {
int ix = s.indexOf(s1);
if (ix >= 0) {
return (s.substring(0, ix) + s2 + replaceAll(s.substring(ix + s1.length()), s1, s2));
} else {
return s;
}
}
}
class ReplaceRecursiveStringBuffer implements Replacer {
public String getMethod() {
return "Recursive with StringBuffer";
}
public String replaceAll(String s, String s1, String s2) {
int ix = s.indexOf(s1);
if (ix >= 0) {
StringBuffer tmp = new StringBuffer("");
tmp.append(s.substring(0, ix));
tmp.append(s2);
tmp.append(s.substring(ix + s1.length()));
return replaceAll(tmp.toString(), s1, s2);
} else {
return s;
}
}
}
class ReplaceRecursiveGlobalStringBuffer implements Replacer {
public String getMethod() {
return "Recursive with global StringBuffer";
}
public String replaceAll(String s, String s1, String s2) {
StringBuffer tmp = new StringBuffer("");
replaceAllHelp(tmp, s, s1, s2);
return tmp.toString();
}
private void replaceAllHelp(StringBuffer res, String s, String s1, String s2) {
int ix = s.indexOf(s1);
if (ix >= 0) {
res.append(s.substring(0, ix));
res.append(s2);
replaceAllHelp(res, s.substring(ix + s1.length()), s1, s2);
} else {
res.append(s);
}
return;
}
}
class ReplaceLoopString implements Replacer {
public String getMethod() {
return "Loop with String";
}
public String replaceAll(String s, String s1, String s2) {
String tmp = new String("");
int pos = 0;
while (pos < s.length()) {
int ix = s.indexOf(s1, pos);
if (ix >= 0) {
tmp = tmp + s.substring(pos, ix) + s2;
pos = ix + s1.length();
} else {
tmp = tmp + s.substring(pos);
pos = s.length();
}
}
return tmp;
}
}
class ReplaceLoopStringBuffer implements Replacer {
public String getMethod() {
return "Loop with StringBuffer";
}
public String replaceAll(String s, String s1, String s2) {
StringBuffer tmp = new StringBuffer("");
int pos = 0;
while (pos < s.length()) {
int ix = s.indexOf(s1, pos);
if (ix >= 0) {
tmp.append(s.substring(pos, ix));
tmp.append(s2);
pos = ix + s1.length();
} else {
tmp.append(s.substring(pos));
pos = s.length();
}
}
return tmp.toString();
}
}
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