选择，插入，冒泡排序
package algorithm;public class SortAlgorithm {private void bubbleSort(int[] numList){//冒泡排序，从前往后扫描，比较相邻两个数的大小，如果发现逆序进行交换int out,in;for(out = numList.length-1;out>1;out--){//从后往前for(in= 0;in<out;in++){if(numList[in]>numList[in+1]){ //当前项大于后一项，交换int temp = numList[in];numList[in] = numList[in+1];numList[in+1] = temp;}}}}private void insertSort(int[] numList){//插入排序，将待排序的数据插入到有序数列中int out,in;//从out处分开数列for(out=1;out<numList.length;out++){int temp = numList[out]; // 待排序的数据in = out-1; //待排序数据的有序数列的最后一个数据while(in>0&&numList[in]>temp){// 当待排序的数据小于数列值时numList[in+1]=numList[in]; //数列向右移一位--in; //指针向左移一位}numList[in+1] = temp; //插入待排序的数据}}private void selectionSort(int[] numList){//选择排序int out,in,temp,min;for(out = 0;out<numList.length-1;out++){min = out;for(in= out+1;in<numList.length;in++){if(numList[in]<numList[min]){min = in;}//交换temp = numList[out];numList[out] = numList[min];numList[min] = numList[out];}}}private void display(int[] numList){for(int j = 0;j<numList.length;j++){System.out.print(numList[j]+" ");}System.out.println();}public static void main(String[] args){SortAlgorithm sort = new SortAlgorithm();int[] numList = new int[]{2,3,56,34,23,89,50};System.out.print("未排序前的数列");sort.display(numList);long begin =System.currentTimeMillis();sort.bubbleSort(numList);long end = System.currentTimeMillis();System.out.print("冒泡排序用时"+(end-begin)+"排序后：");sort.display(numList);begin =System.currentTimeMillis();sort.selectionSort(numList);end = System.currentTimeMillis();System.out.print("选择排序用时"+(end-begin)+"排序后：");sort.display(numList);begin =System.currentTimeMillis();sort.insertSort(numList);end = System.currentTimeMillis();System.out.print("插入排序用时"+(end-begin)+"排序后：");sort.display(numList);}}归并算法：
01.import java.util.Arrays; 02.import java.util.Comparator; 03.public class MergeSort { 04. public static <T> void merge(T[] a, int p, int q, int r, 05. Comparator<? super T> c) { 06. T[] left = Arrays.copyOfRange(a, p, q); 07. T[] right = Arrays.copyOfRange(a, q, r); 08. int indexLeft = 0; 09. int indexRight = 0; 10. for (int i = p; i < r; i++) { 11. if (indexLeft >= left.length) { 12. break; 13. } 14. if (indexRight >= right.length) { 15. System 16. .arraycopy(left, indexLeft, a, i, left.length 17. - indexLeft); 18. break; 19. } 20. if (c.compare(left[indexLeft], right[indexRight]) < 0) { 21. a[i] = left[indexLeft++]; 22. } else { 23. a[i] = right[indexRight++]; 24. } 25. } 26. } 27. public static <T> void mergeSort(T[] a, int p, int r, 28. Comparator<? super T> c) { 29. if (p + 1 < r) { 30. int q = (p + r) / 2; 31. mergeSort(a, p, q, c); 32. mergeSort(a, q + 1, r, c); 33. merge(a, p, q, r, c); 34. } 35. } 36. public static <T> void mergeSort(T[] a, Comparator<? super T> c) { 37. mergeSort(a, 0, a.length, c); 38. } 39. public static void main(String[] args) { 40. // merge's test 41. System.out.println("merge method test"); 42. Integer[] tempMerge = new Integer[] { 1, 4, 7, 11, 14, 17, 2, 4, 6, 8, 43. 10, 20, 30, 40 }; 44. merge(tempMerge, 0, 6, tempMerge.length, new Comparator<Integer>() { 45. @Override 46. public int compare(Integer o1, Integer o2) { 47. return o1 - o2; 48. } 49. }); 50. for (int i : tempMerge) { 51. System.out.print(i + " "); 52. } 53. System.out.println(); 54. // mergeSort's test 55. System.out.println("mergeSort method test"); 56. Integer[] tempMergeSoft = new Integer[] { 5, 2, 4, 6, 1, 3, 2, 6 }; 57. mergeSort(tempMergeSoft, new Comparator<Integer>() { 58. @Override 59. public int compare(Integer o1, Integer o2) { 60. return o1 - o2; 61. } 62. }); 63. for (int i : tempMergeSoft) { 64. System.out.print(i + " "); 65. } 66. System.out.println(); 67. } 68.} 另外：判断一个数是完全平方数，使用Math.floor(Math.sqrt(n))==Math.sqrt(n)
如Math.sqrt(9)==Math.floor(Math.sqrt(9)返回true，因为3.0==3.
回文数即对称数字，可以使用栈来判断。入栈和出栈顺序一样，或者直接进行前后数字的比较
判断一个数是否是2的次幂，用if(((d&(d-1))==0)&&(d!=0))
java中有栈Stack的实现，下面是栈的类继承结构；
类 Stack<E>
java.lang.Object
java.util.AbstractCollection<E>
java.util.AbstractList<E>
java.util.Vector<E>
java.util.Stack<E>