Hashtable

.gitignore

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+# Covers JetBrains IDEs: IntelliJ, RubyMine, PhpStorm, AppCode, PyCharm, CLion, Android Studio and Webstorm
+# Reference: https://intellij-support.jetbrains.com/hc/en-us/articles/206544839
+
+# User-specific stuff:
+.idea/**/workspace.xml
+.idea/**/tasks.xml
+.idea/dictionaries
+
+# Sensitive or high-churn files:
+.idea/**/dataSources/
+.idea/**/dataSources.ids
+.idea/**/dataSources.xml
+.idea/**/dataSources.local.xml
+.idea/**/sqlDataSources.xml
+.idea/**/dynamic.xml
+.idea/**/uiDesigner.xml
+
+# Gradle:
+.idea/**/gradle.xml
+.idea/**/libraries
+
+# CMake
+cmake-build-debug/
+
+# Mongo Explorer plugin:
+.idea/**/mongoSettings.xml
+
+## File-based project format:
+*.iws
+
+## Plugin-specific files:
+
+# IntelliJ
+out/
+
+# mpeltonen/sbt-idea plugin
+.idea_modules/
+
+# JIRA plugin
+atlassian-ide-plugin.xml
+
+# Cursive Clojure plugin
+.idea/replstate.xml
+
+# Crashlytics plugin (for Android Studio and IntelliJ)
+com_crashlytics_export_strings.xml
+crashlytics.properties
+crashlytics-build.properties
+fabric.properties

HashTable.iml

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+<?xml version="1.0" encoding="UTF-8"?>
+<module type="JAVA_MODULE" version="4">
+  <component name="NewModuleRootManager" inherit-compiler-output="true">
+    <exclude-output />
+    <content url="file://$MODULE_DIR$">
+      <sourceFolder url="file://$MODULE_DIR$/src" isTestSource="false" />
+      <sourceFolder url="file://$MODULE_DIR$/test" isTestSource="true" />
+    </content>
+    <orderEntry type="inheritedJdk" />
+    <orderEntry type="sourceFolder" forTests="false" />
+    <orderEntry type="module-library">
+      <library name="JUnit5">
+        <CLASSES>
+          <root url="jar://$APPLICATION_HOME_DIR$/plugins/junit/lib/junit-jupiter-api-5.0.0-RC2.jar!/" />
+          <root url="jar://$APPLICATION_HOME_DIR$/plugins/junit/lib/opentest4j-1.0.0-RC1.jar!/" />
+        </CLASSES>
+        <JAVADOC />
+        <SOURCES />
+      </library>
+    </orderEntry>
+    <orderEntry type="module-library">
+      <library name="testng">
+        <CLASSES>
+          <root url="jar://$APPLICATION_HOME_DIR$/plugins/testng/lib/testng.jar!/" />
+          <root url="jar://$APPLICATION_HOME_DIR$/plugins/testng/lib/jcommander.jar!/" />
+        </CLASSES>
+        <JAVADOC />
+        <SOURCES />
+      </library>
+    </orderEntry>
+  </component>
+</module>

src/ru/spbau/mit/kazakov/HashTable/HashTable.java

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+package ru.spbau.mit.kazakov.HashTable;
+
+/**
+ * HashTable
+ * Key: String
+ * Value: String
+ * Collision resolution: Separate chaining with linked lists
+ */
+public class HashTable {
+    private int capacity = 16;
+    private int size = 0;
+    private LinkedList[] hashtable = new LinkedList[capacity];
+
+    /**
+     * Initialises all linked lists.
+     */
+    public HashTable() {
+        for (int i = 0; i < capacity; i++) {
+            hashtable[i] = new LinkedList();
+        }
+    }
+
+    /**
+     * Returns number of keys in hashtable.
+     */
+    public int size() {
+        return size;
+    }
+
+    /**
+     * Tests if the specified string is a key in this hashtable.
+     */
+    public boolean contains(String key) {
+        int hash = Math.floorMod(key.hashCode(), capacity);
+        return hashtable[hash].contains(key);
+    }
+
+    /**
+     * Returns the value to which the specified key is mapped, or null if this map contains no mapping for the key.
+     */
+    public String get(String key) {
+        int hash = Math.floorMod(key.hashCode(), capacity);
+        return hashtable[hash].get(key);
+    }
+
+    /**
+     * Maps the specified key to the specified value in this hashtable.
+     * Returns previous value to which the specified key was mapped, or null if this map contained no mapping for the key.
+     */
+    public String put(String key, String value) {
+        int hash = Math.floorMod(key.hashCode(), capacity);
+        String returnValue = hashtable[hash].put(key, value);
+
+        if (returnValue == null) {
+            size++;
+            if (size == capacity) {
+                rebuild();
+            }
+        }
+
+        return returnValue;
+    }
+
+    /**
+     * Removes the specified key and its corresponding value from this hashtable.
+     * Returns removed value, or null if this map contained no mapping for the key.
+     */
+    public String remove(String key) {
+        int hash = Math.floorMod(key.hashCode(), capacity);
+        String returnValue = hashtable[hash].remove(key);
+        if (returnValue != null) {
+            size--;
+        }
+        return returnValue;
+    }
+
+    /**
+     * Clears this hashtable so that it contains no keys.
+     */
+    public void clear() {
+        for (int i = 0; i < capacity; i++) {
+            hashtable[i] = new LinkedList();
+        }
+        size = 0;
+    }
+
+    /**
+     * Increases capacity by copying all entries in twice and rehashes all elements.
+     */
+    private void rebuild() {
+        capacity *= 2;
+        size = 0;
+        LinkedList[] oldHashtable = hashtable;
+
+        hashtable = new LinkedList[capacity];
+        for (int i = 0; i < capacity; i++) {
+            hashtable[i] = new LinkedList();
+        }
+
+        for (int i = 0; i < capacity / 2; i++) {
+            while (!oldHashtable[i].empty()) {
+                put(oldHashtable[i].firstElementKey(), oldHashtable[i].firstElementValue());
+                oldHashtable[i].remove(oldHashtable[i].firstElementKey());
+            }
+        }
+    }
+
+}