1.copy
public class Copy { public static void main(String[] args) { int[] a = {3,5,6,87,98,9}; System.out.println("------手工复制-------"); int[] b = new int[a.length]; for (int i=0;i<a.length;i++) { b[i] = a[i]; } System.out.println("-----Arrays.copyOf复制----"); //1参数：源数组，2参数：复制的长度，从0位置开始复制 int[] c = Arrays.copyOf(a, 4); for (int i : c) { System.out.println(i); } System.out.println("---System.arrayCopy-------"); int[] d = new int[10]; //源数组，源数组开始复制的索引位置，目标数组，目标数组的开始插入索引位置，要复制的长度 System.arraycopy(a,1, d, 3, 3); for (int i : d) { System.out.println(i); } } }
2.foreaach遍历
public class Demo { public static void main(String[] args) { int[] a = {1,2,3,4,7,65}; for (int i = 0; i < a.length; i++) { System.out.println(a[i]); } System.out.println("------foreach循环,用来对集合进行遍历（迭代）-----"); for (int temp : a) { System.out.println(temp); } Student[] ss = new Student[3]; ss[0] =new Student(1,"fyt"); ss[1] = new Student(2,"bbb"); ss[2] = new Student(3,"ccc"); for (Student stu : ss) {//声明一个Student类型的变量接收数组中每一个元素 String name = stu.getName(); int id = stu.getId(); System.out.println(id+"--"+name); } } }
3.查找
public class Query1 { public static void main(String[] args) { int[] a = {6,7,9,4,1,5,3}; //查找某个元素在数组中的位置 Query1 q = new Query1(); int index = q.query(a,10); if(index>=0) System.out.println("位置："+index); else System.out.println("不存在"); } public int query(int[] a,int target) { int result = -1; for (int i = 0; i < a.length; i++) { if(a[i]==target) { result = i; break; } } return result; } }
/** * 二分查找 * 前提是：数组已排序 * @author Administrator * */ public class Query2 { public static void main(String[] args) { int[] a = { 6, 7, 9, 4, 1, 5, 3 }; // 1,3,4,5,6,7,9 Arrays.sort(a); // 去数组中查找target变量的值，是否已存在 int index = query(a,1); System.out.println(index); } public static int query(int[] a, int target) { int index = -1; int begin = 0; int end = a.length - 1; while (begin <= end) { int middle = (begin + end) / 2; if (a[middle] > target) { end = middle - 1; } else if (a[middle] < target) { begin = middle + 1; } else { index = middle; break; } } return index; } }
/** * 快速二分查找 * @author Administrator * */ public class Query3 { public static void main(String[] args) { int[] a = { 6, 7, 9, 4, 1, 5, 3 }; // 1,3,4,5,6,7,9 Arrays.sort(a); // Arrays.binarySearch此方法返回值：找到的话返回索引号；找不到的话，查找数据的插入位置为n, 返回-n-1 int index = Arrays.binarySearch(a, 0); System.out.println(index); //toString方法，返回格式化数组 String s= Arrays.toString(a); System.out.println(s); } }
4.排序
/** * 冒泡排序 外层n-1，内层n-1-i * * @author Administrator * */ public class Sort1 { public static void main(String[] args) { int[] a = { 6, 4, 3, 7, 8, 2 }; // 对a数组进行升序排列 // 6,4,3,7,8,2 // 4,6,3,7,8,2--4,3,6,7,8,2--4,3,6,7,8,2--4,3,6,7,8,2--4,3,6,7,2,8 // 4,3,6,7,2,8 // 3,4,6,7,2,8--3,4,6,7,2,8--3,4,6,7,2,8--3,4,6,2,7,8 // 3,4,6,2,7,8 // 3,4,6,2,7,8--3,4,6,2,7,8--3,4,2,6,7,8 // 3,4,2,6,7,8 // 3,4,2,6,7,8--3,2,4,6,7,8 // 3,2,4,6,7,8 // 2,3,4,6,7,8 sort(a); for (int i : a) { System.out.println(i); } } public static void sort(int[] a) { int n = a.length;// 6 for (int i = 0; i < n - 1; i++) { for (int j = 0; j < n - 1 - i; j++) { if (a[j] > a[j + 1]) // 左侧数据大于右侧，交换位置，大的放右边 { int temp = a[j]; a[j] = a[j + 1]; a[j + 1] = temp; } } } } }
/** * 选择排序 * * @author Administrator * */ public class Sort2 { public static void main(String[] args) { int[] a = { 6, 4, 3, 7, 8, 2 }; // 6, 4, 3, 7, 8, 2 // k=0 --k=1--k=2--k=2--k=2--k=5 2, 4, 3, 7, 8, 6 // 2, 4, 3, 7, 8, 6 // k=1 --k=2--k=2--k=2--k=2 2,3,4,7,8,6 // 2,3,4,7,8,6 // k=2 --k=2--k=2--k=2 2,3,4,7,8,6 // 2,3,4,7,8,6 // k=3 --k=3--k=5 2,3,4,6,8,7 // 2,3,4,6,8,7 // k=4 --k=5 2,3,4,6,7,8 sort(a); for (int i : a) { System.out.println(i); } } public static void sort(int[] a) { int n = a.length; for (int i = 0; i < n - 1; i++) { int k = i; for (int j = i + 1; j < n; j++) {// 1-2-3-4-5 if (a[k] > a[j]) { k = j; } } if (k != i) { int temp = a[i]; a[i] = a[k]; a[k] = temp; } } } }
/** * 插入排序 * @author Administrator * */ public class Sort3 { public static void main(String[] args) { int[] a = { 6, 4, 3, 7, 8, 2 }; // yilun:6, 4, 3, 7, 8, 2 // 4, 6, 3, 7, 8, 2 一次 // erlun:4, 6, 3, 7, 8, 2 // 4,3,6,7, 8, 2--3,4,6,7, 8, 2 二次 // sanlun:3,4,6,7, 8, 2 // 3,4,6,7, 8, 2 三次 // ..wulun sort(a); for (int i : a) { System.out.println(i); } } public static void sort(int[] a) { int n = a.length; for (int i = 0; i < n - 1; i++) { for (int j = i + 1; j > 0; j--) {// 2 if (a[j] < a[j - 1]) { int temp = a[j]; a[j] = a[j - 1]; a[j - 1] = temp; } else break; } } } }
/** * 快速排序 使用数组工具类Arrays排序 * * @author Administrator * */ public class Sort4 { public static void main(String[] args) { int[] a = { 6, 4, 3, 7, 8, 2 }; System.out.println("Arrays.sort()升序排"); Arrays.sort(a); for (int i = a.length-1; i >=0; i--) { System.out.println(a[i]); } System.out.println("倒序"); Integer[] a2 = { 6, 4, 3, 7, 8, 2 };// 对象数组 Arrays.sort(a2, Collections.reverseOrder()); for (int i : a2) { System.out.println(i); } } }
/** * 对象数组，按照对象中某个属性进行排序 * @author Administrator * */ public class Sort5 { public static void main(String[] args) { Person[] ps = new Person[4]; ps[0] = new Person("b", 23); ps[1] = new Person("a", 21); ps[2] = new Person("d", 25); ps[3] = new Person("c", 19); //对ps数组，按照人的年龄进行升序排列 int n = ps.length; for (int i = 0; i < n - 1; i++) { for (int j = 0; j < n - 1 - i; j++) { Person p1 = ps[j]; Person p2 = ps[j+1]; if(p1.getAge()>p2.getAge()) { ps[j] = p2; ps[j+1] = p1; } } } for (Person person : ps) { System.out.println(person.getName()+"--"+person.getAge()); } } }