排序
冒泡排序
public class TestDemo {
//冒泡排序
public static void bubbleSort(int[] array) {
boolean val = false;
for (int i = 0; i < array.length - 1; i++) {
for (int j = 0; j < array.length - 1 - i; j++) {
if (array[j] > array[j + 1]) {
int tmp = array[j + 1];
array[j + 1] = array[j];
array[j] = tmp;
val = true;
}
}
if (!val) {
break;
}
}
}
public static void main(String[] args) {
int[] array = {1, 5, 15, 2, 9, 6, 35, 22};
bubbleSort(array);
System.out.println(Arrays.toString(array));
}
}
时间复杂度：
最好情况 O(n) 当输入的数组有序就是最好情况
最坏情况 O(n^2)
稳定性：在输入数组中有两个及以上相同的数，排序结束后数字前后位置不变
稳定
直接插入排序
public class TestDemo {
//直接插入排序
public static void insertSort(int[] array) {
int j = 0;
for (int i = 1; i < array.length; i++) {
int tmp = array[i];
for (j = i - 1; j >= 0; j--) {
if (tmp < array[j]) {
array[j + 1] = array[j];
} else {
break;
}
}
array[j + 1] = tmp;
}
}
public static void main(String[] args) {
int[] array = {1, 5, 15, 2, 9, 6, 35, 22};
insertSort(array);
System.out.println(Arrays.toString(array));
}
}
时间复杂度：
最好情况 O(n)
最坏情况 O(n^2)
稳定性：稳定
选择排序
public class TestDemo {
//选择排序
public static void selectSort(int[] array) {
for (int i = 0; i < array.length; i++) {
for (int j = i + 1; j < array.length; j++) {
if (array[i] > array[j]) {
int tmp = array[j];
array[j] = array[i];
array[i] = tmp;
}
}
}
}
public static void main(String[] args) {
int[] array = {1, 5, 15, 2, 9, 6, 35, 22};
selectSort(array);
System.out.println(Arrays.toString(array));
}
}
时间复杂度：： O(n^2)
稳定性：稳定
二维数组
定义
int[][] array = new int[2][3];
//第一种
int[][] array2 = {{1,2,3},{4,5,6},{7,8,9}};
//第二种
int[][] array3 = new int[2][];
array3[0] = new int[4];
array3[1] = new int[5];
//定义一个不规则数组
二维数组的拷贝
与一维数组相同，四种拷贝方式皆为浅拷贝
以下四种方法二维数组array1的初始值为10
for循环拷贝
class Arr {
private int val = 10;
public void setVal(int val) {
this.val = val;
}
public int getVal() {
return this.val;
}
}
public class TestDemo1 {
public static void main(String[] args) {
Arr[][] array1 = new Arr[2][2];
array1[0][0] = new Arr();
array1[0][1] = new Arr();
array1[1][0] = new Arr();
array1[1][1] = new Arr();
Arr[][] array2 = new Arr[2][2];
for (int i = 0; i < array1.length; i++) {
for (int j = 0; j < array1[i].length; j++) {
array2[i][j] = array1[i][j];
}
}
for (int i = 0; i < array2.length; i++) {
for (int j = 0; j < array2[i].length; j++) {
System.out.print(array2[i][j].getVal() + " ");
}
System.out.println();
}
array2[0][0].setVal(100);
System.out.println("================修改后===============");
for (int i = 0; i < array2.length; i++) {
for (int j = 0; j < array2[i].length; j++) {
System.out.print(array2[i][j].getVal() + " ");
}
System.out.println();
}
System.out.println();
}
}
输出结果：
.clone()
class Arr {
private int val = 10;
public void setVal(int val) {
this.val = val;
}
public int getVal() {
return this.val;
}
}
public class TestDemo1 {
public static void main(String[] args) {
Arr[][] array1 = new Arr[2][2];
array1[0][0] = new Arr();
array1[0][1] = new Arr();
array1[1][0] = new Arr();
array1[1][1] = new Arr();
Arr[][] array2 = new Arr[2][2];
for (int i = 0; i < array1.length; i++) {
array2[i] = array1[i].clone();
for (int j = 0; j < array1[i].length; j++) {
System.out.print(array2[i][j].getVal() + " ");
}
System.out.println();
}
array2[0][0].setVal(100);
System.out.println("================修改后===============");
for (int i = 0; i < array2.length; i++) {
for (int j = 0; j < array2[i].length; j++) {
System.out.print(array2[i][j].getVal() + " ");
}
System.out.println();
}
}
}
输出结果:
Arrays.cpoyOf()
class Arr {
private int val = 10;
public void setVal(int val) {
this.val = val;
}
public int getVal() {
return this.val;
}
}
public class TestDemo1 {
public static void main(String[] args) {
Arr[][] array1 = new Arr[2][2];
array1[0][0] = new Arr();
array1[0][1] = new Arr();
array1[1][0] = new Arr();
array1[1][1] = new Arr();
Arr[][] array2 = new Arr[2][2];
//array2 = Arrays.copyOf(array1, array1.length);
//或者将循环中的Arrays.copyOf方法删掉，用上一行的方法拷贝
for (int i = 0; i < array1.length; i++) {
array2[i] = Arrays.copyOf(array1[i], array1[i].length);
for (int j = 0; j < array1[i].length; j++) {
// array2[j]=array1[j].clone();
System.out.print(array2[i][j].getVal() + " ");
}
System.out.println();
}
array2[0][0].setVal(100);
System.out.println("================修改后===============");
for (int i = 0; i < array2.length; i++) {
for (int j = 0; j < array2[i].length; j++) {
System.out.print(array2[i][j].getVal() + " ");
}
System.out.println();
}
}
}
输出结果：
System.arraycopy()
class Arr {
private int val = 10;
public void setVal(int val) {
this.val = val;
}
public int getVal() {
return this.val;
}
}
public class TestDemo1 {
public static void main(String[] args) {
Arr[][] array1 = new Arr[2][2];
array1[0][0] = new Arr();
array1[0][1] = new Arr();
array1[1][0] = new Arr();
array1[1][1] = new Arr();
Arr[][] array2 = new Arr[2][2];
for (int i = 0; i < array1.length; i++) {
System.arraycopy(array1[i], 0, array2[i], 0, array1[i].length);
for (int j = 0; j < array1[i].length; j++) {
System.out.print(array2[i][j].getVal() + " ");
}
System.out.println();
}
array2[0][0].setVal(100);
System.out.println("================修改后===============");
for (int i = 0; i < array2.length; i++) {
for (int j = 0; j < array2[i].length; j++) {
System.out.print(array2[i][j].getVal() + " ");
}
System.out.println();
}
}
}
输出结果：
