Pre-compile the regex pattern into a Pattern object and reuse

core-java-modules/core-java-text/src/main/java/com/baeldung/pattern/PatternPerformanceComparison.java

@@ -0,0 +1,71 @@
+package com.baeldung.pattern;
+
+import java.time.Duration;
+import java.time.Instant;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+public class PatternPerformanceComparison {
+
+    private static final String PATTERN = "\\d*[02468]";
+    private static List<String> values;
+
+    public static void main(String[] args) {
+        loadValues();
+
+        // 5_000_000 Pattern objects created
+        // 5_000_000 Matcher objects created
+        Instant start = Instant.now();
+        for (String value : values) {
+            value.matches(PATTERN);
+        }
+        System.out.println(Duration.between(start, Instant.now()).toMillis() + "ms -> String.matchs(regex)");
+
+        // Above approach "value.matches(PATTERN)" makes this internally
+        // 5_000_000 Pattern objects created
+        // 5_000_000 Matcher objects created
+        start = Instant.now();
+        for (String value : values) {
+            Pattern.matches(PATTERN, value);
+        }
+        System.out.println(Duration.between(start, Instant.now()).toMillis() + "ms -> Pattern.matches(regex, charSequence)");
+
+        // Above approach "Pattern.matches(PATTERN, value)" makes this internally
+        // 5_000_000 Pattern objects created
+        // 5_000_000 Matcher objects created
+        start = Instant.now();
+        for (String value : values) {
+            Pattern.compile(PATTERN).matcher(value).matches();
+        }
+        System.out.println(Duration.between(start, Instant.now()).toMillis() + "ms -> Pattern.compile(regex).matcher(charSequence).matches()");
+
+        // With pre-compiled pattern
+        // 1         Pattern object created
+        // 5_000_000 Matcher objects created
+        Pattern preCompiledPattern = Pattern.compile(PATTERN);
+        start = Instant.now();
+        for (String value : values) {
+            preCompiledPattern.matcher(value).matches();
+        }
+        System.out.println(Duration.between(start, Instant.now()).toMillis() + "ms  -> preCompiledPattern.matcher(value).matches()");
+
+        //With pre-compiled pattern and reusing the matcher
+        // 1 Pattern object created
+        // 1 Matcher objects created
+        Matcher matcherFromPreCompiledPattern = preCompiledPattern.matcher("");
+        start = Instant.now();
+        for (String value : values) {
+            matcherFromPreCompiledPattern.reset(value).matches();
+        }
+        System.out.println(Duration.between(start, Instant.now()).toMillis() + "ms  -> matcherFromPreCompiledPattern.reset(value).matches()");
+    }
+
+    private static void loadValues() {
+        values = new ArrayList<>();
+        for (int x = 1; x <= 5_000_000; x++) {
+            values.add(String.valueOf(x));
+        }
+    }
+}