我正在做我的作业，我想为我的数组创建一个排序方法。但是，我在排序方法中遇到空指针错误，我不确定为什么。这是我下面的代码。
public Object[] sorted() {
getSetArray();
Arrays.sort(setArray);
return setArray;
}
这些是我的错误 java.lang.NullPointerException 行
java.util.ComparableTimSort.binarySort(ComparableTimSort.java:232) 在
java.util.ComparableTimSort.sort(ComparableTimSort.java:176) 在
java.util.ComparableTimSort.sort(ComparableTimSort.java:146) 在
java.util.Arrays.sort(Arrays.java:472) 在
setadt.SetADT.sorted(SetADT.java:280) 在
setadt.SetADTDriver_sol.main(SetADTDriver_sol.java:233)
package setadt;
import java.util.*;
public class SetADT {
private static Random rand = new Random();
private final int DEFAULT_CAPACITY = 100;
private final int NOT_FOUND = -1;
private int size;
private Object[] setArray;
public SetADT() {
size = 0;
setArray = new Object[DEFAULT_CAPACITY];
}
public SetADT(int capacity) {
size = 0;
setArray = new Object[capacity];
}
public void add(Object newElement) {
if (size() == setArray.length) {
resize();
}
if(!contains(newElement) == true){
setArray[size] = newElement;
size++;
}
//System.out.println(newElement +"\t" + size);
}
public void addAll(SetADT set) {
Object[] temp = set.getSetArray();
for (int i = 0; i < set.size(); i++) {
if (!this.containsValue(temp[i])) {
add(temp[i]);
}
}
}
public boolean contains(Object element) {
for (int i = 0; i < size; i++) {
if (setArray[i].equals(element)) {
return true;
}
}
return false;
}
public boolean containsValue(Object element) {
for (int i = 0; i < size; i++) {
if (setArray[i].toString().equals(element.toString())) {
return true;
}
}
return false;
}
public boolean equals(SetADT set) {
boolean result = false;
Object element;
if (size() == set.size()) {
result = true;
for (int i = 0; i < size(); i++) {
element = setArray[i];
if (!set.contains(element)) {
return false;
}
}
}
return result;
}
public boolean isEmpty() {
if (size == 0) {
return true;
} else {
return false;
}
}
public Object remove(Object element) {
Object result = new Integer(NOT_FOUND);
int search = NOT_FOUND;
if (!isEmpty()) {
for (int i = 0; i < size() && search == NOT_FOUND; i++) {
if (setArray[i].equals(element)) {
search = i;
}
}
if (search != NOT_FOUND) {
result = setArray[search];
setArray[search] = setArray[size - 1];
setArray[size - 1] = null;
size--;
}
}
return result;
}
public Object removeRandom() {
int element;
Object value = new Integer(NOT_FOUND);
if (!isEmpty()) {
element = rand.nextInt(size);
value = setArray[element];
setArray[element] = setArray[size - 1];
setArray[size - 1] = null;
size--;
}
return value;
}
public int size() {
return size;
}
public SetADT union(SetADT set) {
SetADT newSet = new SetADT();
newSet.addAll(this);
newSet.addAll(set);
return newSet;
}
private void resize() {
Object[] newArray = new Object[setArray.length * 2];
for (int i = 0; i < setArray.length; i++) {
newArray[i] = setArray[i];
}
setArray = newArray;
}
public Object[] getSetArray() {
return setArray;
}
public String toString() {
String result = "";
for (int i = 0; i < size(); i++) {
if ((i % 10) == 0 && i != 0) {
result += "\n";
}
result = result + setArray[i].toString() + "\t";
}
return result;
}
public SetADT intersection(SetADT set) {
SetADT newSet = new SetADT();
for(int index = 0; index < set.size; index++){
if(set.contains(set) == set.contains(setArray)){
newSet.add(set);
}
}
return newSet;
}
public SetADT difference(SetADT set) {
SetADT newSet = new SetADT();
for(int index = 0; index < set.size; index++){
if(set.contains(set) == false){
newSet.add(set);
}
}
return newSet;
}
public Object[] sorted() {
setArray = getSetArray();
Arrays.sort(setArray);
return setArray;
}
public static String getObjectArray(Object[] o) {
String s = "";
for (int i = 0; i < o.length; i++) {
s += (o[i] + " ");
}
return s;
}
}
NPE 的原因是您在数组中存储了 null。实施比较Tim排序 http://cr.openjdk.java.net/~martin/webrevs/openjdk7/timsort/src/share/classes/java/util/ComparableTimSort.java.html不检查 null。
private static void binarySort(Object[] a, int lo, int hi, int start) {
214 assert lo <= start && start <= hi;
215 if (start == lo)
216 start++;
217 for ( ; start < hi; start++) {
218 @SuppressWarnings("unchecked")
219 Comparable<Object> pivot = (Comparable) a[start];
220
221 // Set left (and right) to the index where a[start] (pivot) belongs
222 int left = lo;
223 int right = start;
224 assert left <= right;
225 /*
226 * Invariants:
227 * pivot >= all in [lo, left).
228 * pivot < all in [right, start).
229 */
230 while (left < right) {
231 int mid = (left + right) >>> 1;
232 if (pivot.compareTo(a[mid]) < 0)
233 right = mid;
234 else
235 left = mid + 1;
236 }
237 assert left == right;
238
您必须确保数组中不存储空值。
为此，您必须断言方法中传递的参数add不为空，并在排序到有效大小之前创建容器的副本。
public Object[] sorted() {
Object[] toSort = Arrays.copyOf(getSetArray(),getSize());
Arrays.sort(toSort);
return toSort;
}
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