Arrays class
Open
the code : Output a set of arrays
1, _//print array elements Arrays.toString
_System.out .println (Arrays.toString ( a));
package com.array;
import java.util.Arrays;
public class ArrayDoment03 {
public static void main(String[] args) {
int[] a = {1,23,54,78,98,986756};
//打印数组元素Arrays.toString
System.out.println(Arrays.toString(a));//打印输出方法一
printArrays(a);
}
public static void printArrays(int [] a){//打印输出方法二
for (int i = 0; i < a.length; i++){
if(i==0){
System.out.print("[");
}
if(i==a.length-1){
System.out.print(a[i]+"]");
}
else {
System.out.print(a[i]+","+" ");
}
}
}
}
Output result:
[1, 23, 54, 78, 98, 986756]
[1, 23, 54, 78, 98, 986756]
2. Sort the array elements (sort the array through the sort method) Arrays.sort (a); System.out.println ( Arrays.toString
( a ) ) ; Code sample: sort a group of arrays
package com.array;
import java.util.Arrays;
public class ArrayDoment03 {
public static void main(String[] args) {
int[] a = {445,23,89,78,98,986756};
Arrays.sort(a);
System.out.println(Arrays.toString(a));
}
}
output result;
[23, 78, 89, 98, 445, 986756]
3. Fill elements (assignment to the array through the fill method) Arrays.fill
( a,2,4,0); _//The array between 2 and 4 is filled with 0 _System.out.println ( Arrays.toString ( a) ); Code sample: The array between 2 and 4 is filled with 0
package com.array;
import java.util.Arrays;
public class ArrayDoment03 {
public static void main(String[] args) {
int[] a = {445,23,89,78,98,986756};
Arrays.fill(a,fromindex:2,toindex:4,val:0);//2到4之间的数组填充为0
System.out.println(Arrays.toString(a));
}
}
Output result:
[445, 23, 0, 0, 98, 986756]
4. Compare elements (comparing arrays compares whether the elements in the array are equal through the equals method) Arrays.equals
( a,a1); System.out .println ("a
a1:"+(aa1));
System.out.println (“Arrays.equals(a,a1):”+Arrays.equals ( a ,a1)); Code sample: compare array a and array a1
package com.array;
import java.util.Arrays;
public class ArrayDoment03 {
public static void main(String[] args) {
int[] a = {445,23,89,78,98,986756};
int[] a1 ={445,23,89,78,98,986756};
Arrays.equals(a,a1);
System.out.println("a==a1:"+(a==a1));
System.out.println("Arrays.equals(a,a1):"+Arrays.equals(a,a1));
}
}
Output result:
a==a1:false
Arrays.equals(a,a1):true
5. Search subscripts in binary arrays: (binarysearch method to search array subscripts)
int[] sort = new int[]{445,23,89,78,98,986756};
int index = Arrays.binarySearch ( sort,89) ;
System.out .println ("The subscript of 89 is: "+index);
Code sample: output the subscript of 89
package com.array;
import java.lang.reflect.Array;
import java.util.Arrays;
public class ArrayDoment03 {
public static void main(String[] args) {
int[] sort = new int[]{445,23,89,78,98,986756};
int index = Arrays.binarySearch(sort,89);
System.out.println("89的下标是："+index);
}
}
Output result:
Bubble Sort
Code sample:
package com.array;
import java.lang.reflect.Array;
import java.util.Arrays;
public class ArrayDomen07 {
public static void main(String[] args) {
//冒泡排序；要烂熟于心
int[] a ={23,34,45,67,2,12,5,87,98,2345};//程序执行第一步：将实参传入给形参
int[] sort = sort(a);//程序执行第四步：调用序方法以后，返回一个排序后的数组
//调用完我们写的排序方法以后，返回一个排序后的数组
System.out.println(Arrays.toString(sort));//程序执行第五步：得出结果；
//让这里可以输出
}
public static int [] sort(int[] array){//程序执行第二步：将数据传入后，然后在方法体中调用
int temp = 0;
//外循环数组需要排列的次数
for (int i = 0; i < array.length-1; i++){
//内循环比较数组元素中两个数的大小，然后依次循环输出
for (int j = 0; j < array.length-1-i; j++){
if (array[j+1]>array[j]){
temp = array[j];
array[j] = array[j+1];
array[j+1] = temp;
}
}
}
return array;//程序执行第三步：得出结果后将数据返回给数组sort
}
}
Output result:
[2345, 98, 87, 67, 45, 34, 23, 12, 5, 2]
sparse array
What is a sparse array;
when most of the elements in an array are 0, or are arrays with the same value, you can use a sparse array to save the array.
The processing method of sparse array is:
1. Record how many rows and columns the array has, and how many different values there are
2. Record the elements, rows, columns and values with different values in a small-scale array, thereby reducing the scale of the program
Code: before compression
package com.array;
public class ArrayDomeno4 {
public static void main(String[] args) {
int[][] a = new int[11][11];
a[1][2]=1;
a[2][3]=2;
for (int[] ints : a) {
for (int anInt : ints) {
System.out.print(anInt+"\t");
}
System.out.println();
}
}
}
result:
0 0 0 0 0 0 0 0 0 0 0
0 0 1 0 0 0 0 0 0 0 0
0 0 0 2 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0
After converting to a sparse array:
package com.array;
public class ArrayDomeno4 {
public static void main(String[] args) {
int[][] a = new int[11][11];
a[1][2] = 1;
a[2][3] = 2;
System.out.println("输出原始数组：");
for (int[] ints : a) {
for (int anInt : ints) {
System.out.print(anInt + "\t");
}
System.out.println();
}
System.out.println("===========================");
//转换成稀疏数值保存
//1、获取有效值的个数
int sum = 0;
for (int i = 0; i < 11; i++){
for (int j = 0; j < 11; j++){
if (a[i][j]!=0){
sum++;
}
}
}
System.out.println("有效值为："+sum);
//2、创建一个稀疏数组的数组
int[][] a2 = new int[sum+1][3];
a2[0][0] = 11;
a2[0][1] = 11;
a2[0][2] = sum;
//3、遍历二维数组，将非零的值，放到稀疏数组中
int count = 0;
for (int i = 0; i < a.length; i++){
for (int j = 0; j < a[i].length; j++){
if(a[i][j]!=0) {
count++;
a2[count][0] = i;//从第几行第一列存放他的第一个数值
a2[count][1] = j;
a2[count][2] = a[i][j];
}
}
}
//输出稀疏数组；
System.out.println("稀疏数组");
for(int i = 0; i < a2.length; i++){
System.out.println(a2[i][0]+"\t"+a2[i][1]+"\t"+a2[i][2]+"\t");
}
}
}
Output result:
输出原始数组：
0 0 0 0 0 0 0 0 0 0 0
0 0 1 0 0 0 0 0 0 0 0
0 0 0 2 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0
===========================
有效值为：2
稀疏数组
11 11 2
1 2 1
2 3 2