[英]Moving elements from one ArrayList to another
本课中的指示是:完成以下静态方法migrationBlock的定义,该方法对于任何非负整数n,从索引开头的元素开始,从ArrayList fromList的ArrayList中删除n个元素的块,并将它们插入(按顺序)从索引目标开始到ArrayList toList中。 (如果从索引开头到fromList结束的元素少于n个元素,则该方法将从索引开头到结尾的元素移植ArrayList的整个“尾部”。)
到目前为止,我有这个:
public static void transplantBlock( ArrayList<String> fromList,
ArrayList<String> toList,
int start,
int target,
int n ) {
for ( int i = 0; i < n; i++) {
if ( fromList.size() > start) {
fromList.remove(start);
}
}
}
public static void main( String[] args )
{
String[] fromData = { "a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k" };
ArrayList<String> fromList = new ArrayList<String>();
for ( int i = 0; i < fromData.length; i++ )
fromList.add( fromData[ i ] );
String[] toData = { "z", "y", "x", "w", "v", "u", "t", "s" };
ArrayList<String> toList = new ArrayList<String>();
for ( int i = 0; i < toData.length; i++ )
toList.add( toData[ i ] );
transplantBlock( fromList, toList, 6, 3, 4 );
System.out.println( "After:" );
System.out.println( " fromList: " + fromList );
System.out.println( " toList: " + toList );
}
输出应该是这样的:
After:
fromList: [a, b, c, d, e, f, k]
toList: [z, y, x, g, h, i, j, w, v, u, t, s]
我可以从fromList删除正确的元素,但是我不知道如何将它们添加到toList。 如果有人可以帮助我弄清我的缺失,我将非常感激。 谢谢!
(旁注:这是填空作业,所以这不是班级问题)
跟踪索引,将刚刚删除的元素插入到哪里:
int insertIndex = target;
for (int i = 0; i < n; i++) {
if (fromList.size() > start) {
String removed = fromList.remove(start);
toList.add(insertIndex, removed);
insertIndex++;
}
}
有一个add(int index, E element)
在方法List
它看起来应该像这样:
ArrayList<String> myList = new ArrayList(Arrays.asList("a","b","c","d"));
myList.add(2, "x");
// List should look like [a, b, x, c, d] now
其余的应该是微不足道的。
public static void transplantBlock( ArrayList<String> fromList,
ArrayList<String> toList,
int start,
int target,
int n )
{
for (int i = 0; i < n; i++)
{
if (fromList.size() > start)
{
String removed = fromList.remove(start);
toList.add(target, removed);
target++;
}
}
}
public static void main( String[] args )
{
String[] fromData = { "a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k" };
ArrayList<String> fromList = new ArrayList<String>();
for ( int i = 0; i < fromData.length; i++ )
fromList.add( fromData[ i ] );
String[] toData = { "z", "y", "x", "w", "v", "u", "t", "s" };
ArrayList<String> toList = new ArrayList<String>();
for ( int i = 0; i < toData.length; i++ )
toList.add( toData[ i ] );
transplantBlock( fromList, toList, 6, 3, 4 );
System.out.println( "After:" );
System.out.println( " fromList: " + fromList );
System.out.println( " toList: " + toList );
}
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