diff --git a/group20/404130810/src/com/basic/datastructure/ArrayList.java b/group20/404130810/src/com/basic/datastructure/ArrayList.java
new file mode 100644
index 0000000000..8aa4575882
--- /dev/null
+++ b/group20/404130810/src/com/basic/datastructure/ArrayList.java
@@ -0,0 +1,108 @@
+package com.basic.datastructure;
+
+public class ArrayList implements List {
+
+	private Object[] elementData;
+	private int size;
+
+	private int enableCapacity;
+
+	public ArrayList() {
+		this.enableCapacity = 10;
+		this.elementData = new Object[enableCapacity];
+	}
+
+	@Override
+	public void add(Object o) {
+		growIfNeeded();
+		elementData[size] = o;
+		this.size++;
+	}
+
+	@Override
+	public void add(int index, Object o) {
+		rangeCheckForAdd(index);
+		growIfNeeded();
+
+		Object[] tmpObjects = new Object[elementData.length];
+		System.arraycopy(elementData, 0, tmpObjects, 0, index);
+		tmpObjects[index] = o;
+		System.arraycopy(elementData, index, tmpObjects, index + 1, elementData.length - index - 1);
+
+		elementData = tmpObjects;
+
+		this.size++;
+	}
+
+	@Override
+	public Object get(int index) {
+		if (index > size) {
+			throw new IndexOutOfBoundsException("Index: " + index + ", Size: " + size);
+		}
+		return elementData[index];
+	}
+
+	@Override
+	public Object remove(int index) {
+		Object removedObj = this.get(index);
+		rangeCheck(index);
+		Object[] tmpObjects = new Object[elementData.length];
+
+		System.arraycopy(elementData, 0, tmpObjects, 0, index);
+		System.arraycopy(elementData, index + 1, tmpObjects, index, elementData.length - index - 1);
+
+		elementData = tmpObjects;
+
+		return removedObj;
+	}
+
+	@Override
+	public int size() {
+		return size;
+	}
+
+	@Override
+	public String toString() {
+		for (int i = 0; i < elementData.length; i++) {
+			System.out.print(elementData[i] + ",");
+		}
+		return "";
+	}
+
+	private void rangeCheck(int paramInt) {
+		if ((paramInt < 0) || (paramInt >= size)) {
+			throw new IndexOutOfBoundsException(outOfBoundsMsg(paramInt));
+		}
+	}
+
+	private void rangeCheckForAdd(int paramInt) {
+		if ((paramInt < 0) || (paramInt > size)) {
+			throw new IndexOutOfBoundsException(outOfBoundsMsg(paramInt));
+		}
+	}
+
+	private String outOfBoundsMsg(int paramInt) {
+		return "Index: " + paramInt + ", Size: " + size;
+	}
+
+	private Object[] growIfNeeded() {
+		if (enableCapacity <= this.size) {
+			enableCapacity = enableCapacity * 2;
+			Object[] largerElementData = new Object[enableCapacity];
+			System.arraycopy(elementData, 0, largerElementData, 0, elementData.length);
+			elementData = largerElementData;
+		}
+		return elementData;
+	}
+
+	public static void main(String[] args) {
+		ArrayList list = new ArrayList();
+		for (int i = 1; i <= 11; i++) {
+			list.add(String.valueOf(i));
+		}
+		list.add(10,"test");
+		list.get(10);
+		list.remove(10);
+		System.out.println(list);
+	}
+}
diff --git a/group20/404130810/src/com/basic/datastructure/LinkedList.java b/group20/404130810/src/com/basic/datastructure/LinkedList.java
new file mode 100644
index 0000000000..c0981aa8c4
--- /dev/null
+++ b/group20/404130810/src/com/basic/datastructure/LinkedList.java
@@ -0,0 +1,117 @@
+package com.basic.datastructure;
+
+public class LinkedList implements List {
+	private Node first;
+	private Node last;
+
+	private int size;
+
+	public void add(Object o) {
+		addLast(o);
+	}
+
+	public void add(int index, Object o) {
+		checkRange(index);
+		if (index == 0) {
+			addFirst(o);
+		} else if (index == size) {
+			addLast(o);
+		} else {
+
+		}
+	}
+
+	public Object get(int index) {
+		checkRange(index);
+		if(size > 0){
+			int loopTimes = 0;
+			Node p = first;
+			while(index > loopTimes){
+				p = p.next;
+				loopTimes ++;
+			}
+			return p;
+		}
+
+		return null;
+	}
+
+	public Object remove(int index) {
+		return null;
+	}
+
+	public int size() {
+		return size;
+	}
+
+	private void addFirst(Object o) {
+		if (size == 0) {
+			first = new Node(o);
+			last = first;
+		} else {
+			Node tmpNode = new Node(o);
+			tmpNode.next = first;
+			first = tmpNode;
+		}
+		size++;
+	}
+
+	private void addLast(Object o) {
+		if (size == 0) {
+			first = new Node(o);
+			last = first;
+		} else {
+			last.next = new Node(o);
+			last = last.next;
+		}
+		size++;
+	}
+
+	public Object removeFirst() {
+		Node tmpNode = first;
+		first = first.next;
+		size--;
+		return tmpNode;
+	}
+
+	public Object removeLast() {
+		Node tmpNode = last;
+
+		return null;
+	}
+
+	private void checkRange(int index) {
+		if (index > size || index < 0) {
+			throw new IndexOutOfBoundsException("Index: " + index + "Size: " + size);
+		}
+	}
+
+	public String toString() {
+		StringBuilder sb = new StringBuilder();
+		Node p = first;
+		while (p != null) {
+			sb.append(p.item + "\n");
+			p = p.next;
+		}
+		return sb.toString();
+	}
+
+	private static class Node {
+		private Object item;
+		private Node next;
+
+		Node(Object item) {
+			this.item = item;
+		}
+	}
+
+	public static void main(String[] args) {
+		LinkedList list = new LinkedList();
+		for (int i = 0; i < 5; i++) {
+			list.add(i);
+		}
+		list.get(5);
+
+		System.out.println(list);
+	}
+}
diff --git a/group20/404130810/src/com/basic/datastructure/List.java b/group20/404130810/src/com/basic/datastructure/List.java
new file mode 100644
index 0000000000..13fc25acfd
--- /dev/null
+++ b/group20/404130810/src/com/basic/datastructure/List.java
@@ -0,0 +1,10 @@
+package com.basic.datastructure;
+
+public interface List {
+	public void add(Object o);
+	public void add(int index, Object o);
+	public Object get(int index);
+	public Object remove(int index);
+	public int size();
+
+}
diff --git a/group20/404130810/src/com/basic/practice/PolymorphicInJava.java b/group20/404130810/src/com/basic/practice/PolymorphicInJava.java
new file mode 100644
index 0000000000..6bf9996da3
--- /dev/null
+++ b/group20/404130810/src/com/basic/practice/PolymorphicInJava.java
@@ -0,0 +1,41 @@
+package com.basic.practice;
+
+/**
+ * 
+ * @author Wu Alvin
+ * Java Polymorphic Only represent in method level
+ *
+ */
+
+class Fruit{
+	String name = "Fruit";
+	public void print(int i){
+		System.out.println("Fruit" + i);
+	}
+}
+
+
+class Apple extends Fruit{
+	String name = "Apple";
+	public void print(int i){
+		System.out.println("Apple" + i);
+	}
+}
+
+
+public class PolymorphicInJava {
+	
+	public static void main(String[] args) {
+		Apple apple = new Apple();
+		apple.print(100);
+		//Apple100
+		System.out.println(apple.name);
+		//Apple
+		Fruit fruit = apple;
+		fruit.print(100);
+		//Apple100
+		System.out.println(fruit.name);
+		//Fruit
+	}
+
+}
diff --git a/group20/404130810/src/com/basic/practice/ValuePassInJava.java b/group20/404130810/src/com/basic/practice/ValuePassInJava.java
new file mode 100644
index 0000000000..6187b5e0fc
--- /dev/null
+++ b/group20/404130810/src/com/basic/practice/ValuePassInJava.java
@@ -0,0 +1,44 @@
+package com.basic.practice;
+
+public class ValuePassInJava {
+
+	/*
+	 * Pass the Simple value, etc int String...
+	 * Change will NOT happened
+	 * 
+	*/ 
+	public static void main(String[] args) {
+		String s = new String("123");
+		int i = 1;
+		changeVal(i);
+		System.out.println(i);
+		
+	}
+	
+	private static void changeVal(int i){
+		i = 2;
+	}
+	
+	/*
+	 * Pass whole OBJECT, but change the Member variable
+	 * Change will happened
+	 */
+	
+	/*
+	public static void main(String[] args) {
+		Person p = new Person();
+		p.age = 10;
+		changeAge(p);
+		System.out.println(p.age);
+	}
+	
+	private static void changeAge(Person p){
+		p.age = 20;
+	}
+	*/
+	
+}
+
+class Person{
+	int age;
+}