Java

Question

我想知道 ArrayList 的 UnorderedList 的方法是什么样的。我知道我们会有 addToFront、addToRear 和 addAfter（都带有 T 元素），但我只见过用数组实现的（见下文）。是否可以改用 ArrayList？这将如何改变方法？希望我的问题有道理。

这是我遇到的代码：

public void addToFront(T element) {

    if (size() == list.length) {
        expandCapacity();
    }

    for (int i = this.size(); i > 0; i--) {
        this.list[i] = this.list[i-1];
    }

    this.list[0] = element;
    this.rear++;
}

/**
 * Adds the specified element to the rear of this list.
 *
 * @param element  the element to be added to the list
 */
public void addToRear(T element) {
    if (size() == list.length) {
        expandCapacity();
    }

    this.list[rear] = element;
    this.rear++;
}

/**
 * Adds the specified element after the specified target element.
 * Throws an ElementNotFoundException if the target is not found.
 *
 * @param element  the element to be added after the target element
 * @param target   the target that the element is to be added after
 */
public void addAfter(T element, T target) {
    if (size() == list.length) {
        expandCapacity();
    }

    int scan = 0;
    while (scan < rear && !target.equals(list[scan])) {
        scan++;
    }

    if (scan == rear) {
        throw new ElementNotFoundException("list");
    }

    scan++;
    for (int scan2 = rear; scan2 > scan; scan2--) {
        list[scan2] = list[scan2 - 1];
    }

    list[scan] = element;
    rear++;
}
}

Answer 1

ArrayList 抽象了过渡数组的大小管理方面。查看：

http://docs.oracle.com/javase/7/docs/api/java/util/ArrayList.html#add(int,%20E)

import java.util.ArrayList;

public class Test<T> {
  ArrayList<T> yourArray;

  Test() {
    // Initialize to avoid NPEs
    yourArray = new ArrayList<T>();
  }

  public void addToFront(T element) {
    yourArray.add(0, element);
  }

  public void addToRear(T element) {
     yourArray.add(yourArray.size(), element);
  }

  public void addAfter(T element, T target) {
     yourArray.add(yourArray.indexOf(target) + 1, element);
  }

  public void addBefore(T element, T target) {
     final int location = yourArray.indexOf(target);

     if (location == 0) {
       addToFront(element);
     } else {
       yourArray.add(yourArray.indexOf(target) - 1, element);
     }
  }
}

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