CodeGym-17~20

0.如果是基本数据类型的话，在数组中就存储特定的值；如果是对象的话，在数组中就是存储对象的引用。

1.数组本身就是对象

0.Arrays.sort(array);　　Arrays.toString(array);(重写了toString方法)　　Arrays.copyOf(array,length);(返回复制以后的数组,也可以复制二维数组)　　Arrays.copyOfRange(array, start_index,end_index);

1.数组类并没有重写equals方法，但是Arrays类重写了equals方法。Arrays.equals(array1,array2);　　Arrays.deepEquals(array1,array2);　　Arrays.deepToString(array1,array2);

又读文章

　　　　ArrayList的size不定的根据：

When the internal array is filled, ArrayList creates a new array internally. The size of the new array is the size of the old array times 1.5 plus 1.

All the data is copied from the old array into the new one。

The old array is cleaned up by the garbage collector.

　　indexOf();　　get();　　add();　　contain();　　set();(与add有区别)　　clear();　　asList();{ArrayList<Cat> catsList = new ArrayList<>(Arrays.asList(catsArray));(使用方法)}　　toArray();

　　size();　　

1.未解决问题：ArrayList<Cat> cats = new ArrayList<>(); ArrayList<Cat> cats = new ArrayList<Cat>();两者区别

最后再读一篇

0.You cannot simultaneously iterate over a collection and change its elements.（不能同时迭代集合并更改其中的元素，包括插入，删除等操作）

要实现迭代时还要更改其中的内容，就要用到Iterator类

hasNext() - returns true or false, depending on whether there is a next item in the list, or we have already reached the last one.
next() - returns the next item in the list
remove() - removes an item from the list

Iterator<Cat> catIterator = cats.iterator();// Create an iterator

while(catIterator.hasNext()) {// As long as there are elements in the list

   Cat nextCat = catIterator.next();// Get the next element

   System.out.println(nextCat);// Display it

}

关于remove（）方法：remove() removes the last element returned by the iterator.

remove（）方法的使用：

Iterator<Cat> catIterator = cats.iterator();// Create an iterator

while(catIterator.hasNext()) {// As long as there are elements in the list

   Cat nextCat = catIterator.next();// Get the next element

   if (nextCat.name.equals("Lionel Messi")) {

       catIterator.remove();// Delete the cat with the specified name

   }

}

System.out.println(cats);

巴特西

CodeGym-17~20

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