Java按顺序将数字插入数组

Question

import java.util.*;

public class MyArrayList {
private Object[]buffer;
private int currentSize;

public MyArrayList(){
   final int INITIAL_SIZE=10;
  buffer = new Object[INITIAL_SIZE];
  currentSize=0;
  }

public int size() {
  return currentSize;
  }

private void checkBounds(int n){
  if (n<0||n>= currentSize){
     throw new IndexOutOfBoundsException();
     }
  }
public Object get (int pos){
  checkBounds(pos);
  return buffer[pos];
  }
public Object remove(int pos){
  checkBounds(pos);
  Object removed = buffer[pos];
  for (int i = pos+1; i < currentSize; i++){
     buffer[i-1] = buffer[i];
  }
  currentSize--;
  return removed;
}
public boolean add(int pos, Object newElement){
  growBufferIfNecessary();
  currentSize++;
  checkBounds(pos);
  for(int i = currentSize - 1; i > pos; i--){
     buffer[i] = buffer [i-1];
  }
  buffer[pos] = newElement;
  return true;
}
public boolean addLast(Object newElement){
  growBufferIfNecessary();
  currentSize++;
  buffer[currentSize -1] = newElement;
  return true;
}
 private void growBufferIfNecessary(){
  if (currentSize==buffer.length){
     Object[] newBuffer = new Object[2*buffer.length];
     for(int i=0; i<buffer.length; i++){
     newBuffer[i] = buffer[i];
     }
  buffer = newBuffer;
   }
} 

}

清单插入（5）；插入（10）；插入（8）；插入（20）；插入（6）；

如果现在打印列表，它应该打印为：

5

 import java.util.*;

 public class ArrayListHomework {
 public static void main (String[]args){
 MyArrayList list = new MyArrayList();

 list.insert(5);
 list.insert(10);
 list.insert(8);
 list.insert(20);
 list.insert(6);
 for (int i=0; i<list.size(); i++){

     System.out.println(list.get(i));

   }
  }  
 }

Answer 1

遗憾的是，您的“教授”提供的代码在add()方法中有一个bug，这是不可原谅的，如下所示：

public boolean add(int pos, Object newElement){
    growBufferIfNecessary();
    currentSize++;
    checkBounds(pos);
    // rest of method

因为没有首先调用checkbounds()，所以如果pos越界，currentsize将增加（缓冲区不必要地增加），从而使实例处于不一致/错误的状态。

编码101：首先，检查参数。

public boolean add(int pos, Object newElement){
    checkBounds(pos);
    growBufferIfNecessary();
    currentSize++;
    // rest of method