[mask-string-except-last-4] mask str (#17661)

* [mask-string-except-last-4] mask str

* [mask-string-except-last-4] move to a new module

Author: sk1418

core-java-modules/core-java-string-operations-11/README.md

@@ -0,0 +1,2 @@
+
+### Relevant Articles:

core-java-modules/core-java-string-operations-11/pom.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <artifactId>core-java-string-operations-11</artifactId>
+    <packaging>jar</packaging>
+    <name>core-java-string-operations-11</name>
+    <parent>
+        <groupId>com.baeldung.core-java-modules</groupId>
+        <artifactId>core-java-modules</artifactId>
+        <version>0.0.1-SNAPSHOT</version>
+    </parent>
+</project>

core-java-modules/core-java-string-operations-11/src/test/java/com/baeldung/maskstring/MaskStringUnitTest.java

@@ -0,0 +1,79 @@
+package com.baeldung.maskstring;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.util.Arrays;
+
+import org.junit.jupiter.api.Test;
+
+public class MaskStringUnitTest {
+
+    private static final String INPUT_1 = "a b c d 1234";
+    private static final String INPUT_2 = "a b c d     ";
+    private static final String INPUT_3 = "a b";
+
+    private static final String EXPECTED_1 = "********1234";
+    private static final String EXPECTED_2 = "********    ";
+    private static final String EXPECTED_3 = "a b";
+
+    public String maskByCharArray(String input) {
+        if (input.length() <= 4) {
+            return input;
+        }
+        char[] chars = input.toCharArray();
+        Arrays.fill(chars, 0, chars.length - 4, '*');
+        return new String(chars);
+    }
+
+    @Test
+    void whenUsingCharArray_thenCorrect() {
+        assertEquals(EXPECTED_1, maskByCharArray(INPUT_1));
+        assertEquals(EXPECTED_2, maskByCharArray(INPUT_2));
+        assertEquals(EXPECTED_3, maskByCharArray(INPUT_3));
+    }
+
+    public String maskBySubstring(String input) {
+        if (input.length() <= 4) {
+            return input;
+        }
+        String toMask = input.substring(0, input.length() - 4);
+        String keepPlain = input.substring(input.length() - 4);
+        return toMask.replaceAll(".", "*") + keepPlain;
+    }
+
+    @Test
+    void whenUsingSubstring_thenCorrect() {
+        assertEquals(EXPECTED_1, maskBySubstring(INPUT_1));
+        assertEquals(EXPECTED_2, maskBySubstring(INPUT_2));
+        assertEquals(EXPECTED_3, maskBySubstring(INPUT_3));
+    }
+
+    public String maskByRegex(String input) {
+        if (input.length() <= 4) {
+            return input;
+        }
+        return input.replaceAll(".(?=.{4})", "*");
+    }
+
+    @Test
+    void whenUsingRegex_thenCorrect() {
+        assertEquals(EXPECTED_1, maskByRegex(INPUT_1));
+        assertEquals(EXPECTED_2, maskByRegex(INPUT_2));
+        assertEquals(EXPECTED_3, maskByRegex(INPUT_3));
+    }
+
+    public String maskByRepeat(String input) {
+        if (input.length() <= 4) {
+            return input;
+        }
+        int maskLen = input.length() - 4;
+        return "*".repeat(maskLen) + input.substring(maskLen);
+    }
+
+    @Test
+    void whenUsingRepeat_thenCorrect() {
+        assertEquals(EXPECTED_1, maskByRepeat(INPUT_1));
+        assertEquals(EXPECTED_2, maskByRepeat(INPUT_2));
+        assertEquals(EXPECTED_3, maskByRepeat(INPUT_3));
+    }
+}

core-java-modules/pom.xml

@@ -217,6 +217,7 @@
         <module>core-java-string-operations-8</module>
         <module>core-java-string-operations-9</module>
         <module>core-java-string-operations-10</module>
+        <module>core-java-string-operations-11</module>
         <module>core-java-regex</module>
         <module>core-java-regex-2</module>
         <module>core-java-regex-3</module>