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MyArrayList.java
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146 lines (126 loc) · 2.96 KB
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import java.util.Arrays;
import java.util.NoSuchElementException;
public class MyArrayList<E> {
private E[] data;
private int size;
private static final int INIT_CAP = 1;
public MyArrayList() {
this(INIT_CAP);
}
@SuppressWarnings("unchecked")
public MyArrayList(int initCapacity) {
data = (E[]) new Object[initCapacity];
size = 0;
}
@SuppressWarnings("unchecked")
private void resize(int newCap) {
E[] temp = (E[]) new Object[newCap];
for (int i = 0; i < size; i++) {
temp[i] = data[i];
}
data = temp;
}
@SuppressWarnings("unused")
private void display() {
System.out.println("size = " + size + " cap = " + data.length);
System.out.println(Arrays.toString(data));
}
private boolean isElementIndex(int index) {
return index >= 0 && index < size;
}
private boolean isPositionIndex(int index) {
return index >= 0 && index <= size;
}
private void checkElementIndex(int index) {
if (!isElementIndex(index)) {
throw new IndexOutOfBoundsException("Index: " + index + ", Size: " + size);
}
}
private void checkPositionIndex(int index) {
if (!isPositionIndex(index)) {
throw new IndexOutOfBoundsException("Index: " + index + ", Size: " + size);
}
}
public void addLast(E e) {
int cap = data.length;
if (size == cap) {
resize(2 * cap);
}
data[size] = e;
size++;
}
public void add(int index, E e) {
checkPositionIndex(index);
int cap = data.length;
if (size == cap) {
resize(cap * 2);
}
for (int i = size; i > index; i--) {
data[i] = data[i - 1];
}
data[index] = e;
size++;
}
public void addFirst(E e) {
add(0, e);
}
// 删除元素
public E removeLast() {
if (size == 0) {
throw new NoSuchElementException();
}
int cap = data.length;
if (size <= cap / 4) {
resize((cap / 2));
}
E deleteVal = data[size - 1];
data[size - 1] = null;
size--;
return deleteVal;
}
public E remove(int index) {
checkElementIndex(index);
int cap = data.length;
if (size <= cap / 4) {
resize(cap / 2);
}
E deleteVal = data[index];
for (int i = index + 1; i < size; i++) {
data[i - 1] = data[i];
}
data[size - 1] = null;
size--;
return deleteVal;
}
public E removeFirst() {
return remove(0);
}
public E get(int index) {
checkElementIndex(index);
return data[index];
}
public E set(int index, E e) {
checkElementIndex(index);
E oldVal = data[index];
data[index] = e;
return oldVal;
}
public int size() {
return size;
}
public boolean isEmpty() {
return size == 0;
}
public static void main(String[] args) {
MyArrayList<Integer> arr = new MyArrayList<>(3);
for (int i = 1; i <= 5; i++) {
arr.addLast(i);
}
arr.remove(3);
arr.add(1, 9);
arr.addFirst(100);
for (int i = 0; i < arr.size(); i++) {
System.out.println(arr.get(i));
}
}
}