谢谢大家的回复。我写了一个名为reverse2的方法,至少适用于实现类ArrayList和LinkedList。不确定它效率如何。
import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;
import java.util.ListIterator;
import java.util.Arrays;
public class ReverseDemo {
public static <T> List<T> reverse1(List<T> list) {
List<T> reversed = new ArrayList<T>();
for (int i = list.size() - 1; i > -1; i--) {
reversed.add(list.get(i));
}
return reversed;
}
public static <T> List<T> reverse2(List<T> list) {
int size = list.size();
ArrayList<T> obArray = new ArrayList<T>();
obArray.addAll(list);
ListIterator<T> iter = list.listIterator();
for (int i = 0; i < size; i++) {
iter.next();
iter.set(obArray.get(size - 1 - i));
}
return list;
}
public static void main(String[] args) {
LinkedList<Integer> linkedInt = new LinkedList<Integer>();
ArrayList<Double> arrayDouble = new ArrayList<Double>();
for (int k = 0; k < 10; k++) {
double doubleNum = 10*Math.random();
int intNum = (int) (10*Math.random());
linkedInt.add(intNum);
arrayDouble.add(doubleNum);
}
TextIO.putln("Testing reverse1.");
System.out.println(Arrays.toString(linkedInt.toArray()));
System.out.println(Arrays.toString(reverse1(linkedInt).toArray()));
TextIO.putln("LinkedList structure preserved?");
System.out.println(reverse1(linkedInt) instanceof LinkedList<?>);
System.out.println(Arrays.toString(arrayDouble.toArray()));
System.out.println(Arrays.toString(reverse1(arrayDouble).toArray()));
TextIO.putln("ArrayList structure preserved?");
System.out.println(reverse1(arrayDouble) instanceof ArrayList<?>);
TextIO.putln("\nTesting reverse2.");
System.out.println(Arrays.toString(linkedInt.toArray()));
System.out.println(Arrays.toString(reverse2(linkedInt).toArray()));
TextIO.putln("LinkedList structure preserved?");
System.out.println(reverse2(linkedInt) instanceof LinkedList<?>);
System.out.println(Arrays.toString(arrayDouble.toArray()));
System.out.println(Arrays.toString(reverse2(arrayDouble).toArray()));
TextIO.putln("ArrayList structure preserved?");
System.out.println(reverse2(arrayDouble) instanceof ArrayList<?>);
}
}
控制台输出:
测试 reverse1。
[8, 0, 1, 9, 3, 4, 3, 7, 6, 3]
[3, 6, 7, 3, 4, 3, 9, 1, 0, 8]
LinkedList 结构被保留了吗?
false
[8.301783107294664, 5.434068303620735, 9.095396759542615, 0.41823972682620836, 9.56659902304762, 3.2560723280079085, 4.037362000077436, 9.731919590391389, 0.5243645318825874, 5.9432185528462975]
[5.9432185528462975, 0.5243645318825874, 9.731919590391389, 4.037362000077436, 3.2560723280079085, 9.56659902304762, 0.41823972682620836, 9.095396759542615, 5.434068303620735, 8.301783107294664]
ArrayList 结构被保留了吗?
true
测试reverse2。
[8, 0, 1, 9, 3, 4, 3, 7, 6, 3]
[3, 6, 7, 3, 4, 3, 9, 1, 0, 8]
链表结构保持不变?
是
[8.301783107294664,5.434068303620735,9.095396759542615,0.41823972682620836,9.56659902304762,3.2560723280079085,4.037362000077436,9.731919590391389,0.5243645318825874,5.9432185528462975]
[5.9432185528462975,0.5243645318825874,9.731919590391389,4.037362000077436,3.2560723280079085,9.56659902304762,0.41823972682620836,9.095396759542615,5.434068303620735,8.301783107294664]
数组列表结构保持不变?
是