将String添加到String数组的开头
是否可以在不迭代整个数组的情况下将字符串添加到String数组的开头。
唯一的方法是维护一个环形缓冲区。 即你有一个计数器，它记住开始的位置，你移动它而不是移动数组中的所有条目。 这只能起作用，因为你重新定义了“开始”的含义。
请参阅ArrayDeque的源代码，其中包含三个字段
86 /** 87 * The array in which the elements of the deque are stored. 88 * The capacity of the deque is the length of this array, which is 89 * always a power of two. The array is never allowed to become 90 * full, except transiently within an addX method where it is 91 * resized (see doubleCapacity) immediately upon becoming full, 92 * thus avoiding head and tail wrapping around to equal each 93 * other. We also guarantee that all array cells not holding 94 * deque elements are always null. 95 */ 96 private transient E[] elements; 97 98 /** 99 * The index of the element at the head of the deque (which is the 100 * element that would be removed by remove() or pop()); or an 101 * arbitrary number equal to tail if the deque is empty. 102 */ 103 private transient int head; 104 105 /** 106 * The index at which the next element would be added to the tail 107 * of the deque (via addLast(E), add(E), or push(E)). 108 */ 109 private transient int tail;
所以添加到开始就像这样
224 public void addFirst(E e) { 225 if (e == null) 226 throw new NullPointerException(); 227 elements[head = (head - 1) & (elements.length - 1)] = e; 228 if (head == tail) 229 doubleCapacity(); 230 } 312 /** 313 * @throws NoSuchElementException {@inheritDoc} 314 */ 315 public E getFirst() { 316 E x = elements[head]; 317 if (x == null) 318 throw new NoSuchElementException(); 319 return x; 320 }
注意：它移动头部而不是将所有元素向下移动到arrays中。
尝试
String[] a = {"1", "2"}; String[] a2 = new String[a.length + 1]; a2[0] = "0"; System.arraycopy(a, 0, a2, 1, a.length);
如果您已经在使用Guava，可以使用ObjectArrays::concat来执行此操作：
String[] args = ...; ObjectArrays.concat("prepended", args);
你不能……你必须移动它前面的所有字符串以容纳新的字符串。 如果您直接将其添加到第0个索引，那么您将丢失之前的元素
这是@matteosilv提出的解决方案的更正版本：
String[] myArray= {"hi","hi2"}; List list = new LinkedList (Arrays.asList(myArray)); list.add(0, "h3"); myArray = list.toArray(new String[list.size()]);
String[] myArray= {"hi","hi2"}; List temp = new ArrayList (Arrays.asList(prova)); temp.add(0, "h3"); myArray = temp.toArray(new String[temp.size()]);
为此，您应该使用List 。
如果你想特别使用内部数组，那就去找一个ArrayList
我最好能管理……
public static void main(String[] args) { String[] s = new String[] { "a", "b", "c" }; System.out.println(Arrays.toString(prepend(s,"d"))); } public static String[] prepend(String[] a, String el) { String[] c = new String[a.length+1]; c[0] = el; System.arraycopy(a, 0, c, 1, a.length); return c; }
你可以做下面的事情
public class Test { public static String[] addFirst(String s[], String e) { String[] temp = new String[s.length + 1]; temp[0] = e; System.arraycopy(s, 0, temp, 1, s.length); return temp; } public static void main(String[] args) { String[] s = { "b", "c" }; s = addFirst(s, "a"); System.out.println(Arrays.toString(s)); } }