1.一维数组的使用
1）一维数组的声明和初始化
2）如何调用数组的指定位置的元素
3）如何获取数组的长度
4）如何遍历数组
public class ArrayTest {
public static void main(String[] args) {
//一维数组的声明和初始化；
int[] ids;
ids = new int[]{1001,1002,1003,1004};//1.1静态初始化:数组的初始化和数组元素的赋值操作同时进行
//也是正确的：
int[] ide = {1,2,3,4,5};//类型推断
int ida[] = {1,2,3,4,5};//中括号位置可以更改
//1.2动态初始化：数组的初始化和数组元素的赋值操作分开进行
String[] names = new String[5];
//总结:数组一旦初始化完成，其长度就确定了
//2.如何调用数组的指定位置的元素:通过角标（索引）的方式调用
names[0] = "Vlahovic";
names[1] = "Pogba";
names[2] = "Mbappe";
names[3] = "Halland";
names[4] = "Cristiano";
//3.如何获取数组的长度。属性：length
System.out.println(names.length);
System.out.println(ids.length);
//4.如何遍历数组元素
int i;
for(i = 0;i < names.length;i++)
{
System.out.println(names[i]);
}
}
}
5）数组元素的默认初始化值
public class ArrayTest1 {
public static void main(String[] args) {
//5.数组元素的默认初始化值
int i;
int[] arr = new int[4];
for(i = 0;i < arr.length;i++)
{
System.out.println(arr[i]);
}
short[] arr1 = new short[4];
for(i = 0;i < arr1.length;i++)
{
System.out.println(arr1[i]);
}//数组元素是整形：0
float[] arr2 = new float[4];
for(i = 0;i < arr2.length;i++)
{
System.out.println(arr2[i]);
}//数组元素为浮点型：0.0
char[] arr3 = new char[4];
for(i = 0;i < arr3.length;i++)
{
System.out.println("----" + arr3[i] + "----");
}//数组元素为字符型：类似于空格的符号
boolean[] arr4 = new boolean[4];
for(i = 0;i < arr4.length;i++)
{
System.out.println(arr4[i]);
}//数组元素为boolean：false
String[] arr5 = new String[4];
for(i = 0;i < arr5.length;i++)
{
System.out.println(arr5[i]);
}//数组元素为引用数据类型：null
}
}
6）数组的内存解析
数组地址在栈空间，赋值留在堆空间内
TEST2:
import java.util.Scanner;
public class FindGrade {
public static void main(String[] args) {
Scanner scanf_s = new Scanner(System.in);
System.out.println("请输入学生人数：");
int num1 = scanf_s.nextInt();
int[] score = new int[num1];
char[] grade = new char[num1];
int i, maxScore = 0;
System.out.println("请输入" + num1 + "个学生的成绩：");
for(i = 0;i < score.length;i++)
{
score[i] = scanf_s.nextInt();
}
for(i = 0;i < score.length;i++)
{
if(maxScore < score[i])
{
maxScore = score[i];
}
}
System.out.println("最高分是" + maxScore);
for(i = 0;i < score.length;i++)
{
if(score[i] >= (maxScore - 10))
{
grade[i] = 'A';
}else if(score[i] >= (maxScore -20))
{
grade[i] = 'B';
}else if(score[i] >= (maxScore - 30))
{
grade[i] = 'C';
}else
{
grade[i] = 'D';
}
}
for(i = 0;i < score.length;i++)
{
System.out.println("student " + i + " score is " + score[i] + " grade is " + grade[i]);
}
}
}
2.二维数组的使用（数组的元素又是数组）
1）二维数组的声明和初始化
2）如何调用数组的指定位置的元素
3）如何获取数组的长度
4）如何遍历数组
5）数组元素的默认初始化值
package com.atguigu.java;
public class ArrayTest3 {
public static void main(String[] args) {
//数组元素的默认初始化值
int[][] arr = new int[4][3];
System.out.println(arr[0]);//地址值
System.out.println(arr[0][0]);
int[][] arr1 = new int[4][];
System.out.println(arr1[4]);//null
}
}
6）数组的内存解析
public class ArrayTest2 {
public static void main(String[] args) {
//1.二维数组的声明和初始化
int[] arr = new int[]{1,2,3};//一维数组
//静态初始化
int[][] arr1 = new int[][]{{1,2,3},{4,5,6}};
//动态初始化1
String[][] arr2 = new String[3][2];
//动态初始化2
String[][] arr3 = new String[3][];
int[] arr4[] = new int[][]{{1,2,3},{4,5},{6,7,8}};
//2.如何调用数组指定位置的元素
System.out.println(arr1[0][1]);//2
System.out.println(arr2[1][1]);//null
arr3[1] = new String[4];//
System.out.println(arr3[1][0]);
//3.获取数组的长度
System.out.println(arr4.length);//3
System.out.println(arr4[1].length);//2
System.out.println();
//4.如何遍历2维数组
int i, j;
for(i = 0;i < arr4.length;i++)
{
for(j = 0;j < arr4[i].length;j++)
{
System.out.println(arr4[i][j]);
}
}
}
}
public class ArrayTest2 {
public static void main(String[] args) {
//1.二维数组的声明和初始化
int[] arr = new int[]{1,2,3};//一维数组
//静态初始化
int[][] arr1 = new int[][]{{1,2,3},{4,5,6}};
//动态初始化1
String[][] arr2 = new String[3][2];
//动态初始化2
String[][] arr3 = new String[3][];
int[] arr4[] = new int[][]{{1,2,3},{4,5},{6,7,8}};
//2.如何调用数组指定位置的元素
System.out.println(arr1[0][1]);//2
System.out.println(arr2[1][1]);//null
arr3[1] = new String[4];//
System.out.println(arr3[1][0]);
//3.获取数组的长度
System.out.println(arr4.length);//3
System.out.println(arr4[1].length);//2
System.out.println();
//4.如何遍历2维数组
int i, j;
for(i = 0;i < arr4.length;i++)
{
for(j = 0;j < arr4[i].length;j++)
{
System.out.println(arr4[i][j]);
}
}
}
}
打印杨辉三角：
import java.util.Scanner;
public class YanghuiTriangle {
public static void main(String[] args) {
Scanner scanf_s = new Scanner(System.in);
System.out.println("请输入要打印的杨辉三角的行数：");
int n = scanf_s.nextInt();
int[][] yanghui = new int[n][n];
int i, j;
for(i = 0;i < n;i++)
{
yanghui[i][0] = 1;
yanghui[i][i] = 1;
}
for(i = 2;i < n;i++)
{
for(j = 1;j <= i - 1;j++)
{
yanghui[i][j] = yanghui[i-1][j-1] + yanghui[i-1][j];
}
}
for(i = 0;i < n;i++)
{
for(j = 0;j <= i;j++)
{
System.out.print(yanghui[i][j] + " ");
}
System.out.println();
}
}
}
3.数组中涉及到的常用算法
1.数组元素的赋值
package com.atguigu.test;
public class SetValue {
public static void main(String[] args) {
int[] arr = new int[6];
int i, j;
for(i = 0;i < arr.length;i++)
{
arr[i] = (int) (Math.random() * 30) + 1;
for(j = 0;j < i;j++)
{
if(arr[j] == arr[i])
{
i--;
break;
}
}
}
for(i = 0;i < arr.length;i++)
{
System.out.println(arr[i]);
}
}
}
2.数组的复制、反转、查找
package com.atguigu.exer;
public class ArrayCopy {
public static void main(String[] args) {
int[] array1 ,array2;
array1 = new int[]{1,3,5,7,8};
array2 = new int[array1.length];
for(int i = 0;i < array1.length;i++)
{
array2[i] = array1[i];
}
//输出
for(int i = 0;i < array1.length;i++)
{
System.out.println(array2[i]);
}
System.out.println();
for(int i = 0;i < array1.length / 2;i++)//终止条件为array1.length / 2,防止反转两遍
{
int temp = array1[i];
array1[i] = array1[array1.length - i - 1];
array1[array1.length - i - 1] = temp;
}
//输出
for(int i = 0;i < array1.length;i++)
{
System.out.println(array1[i]);
}
System.out.println();
String[] arr = new String[]{"JJ","DD","MM","BB","GG","AA"};
String dest = "BB";
boolean isFlag = true;
for(int i = 0;i dest1)
{
end = middle - 1;
}
else
{
head = middle + 1;
}
}
if(isFlag1)
{
System.out.println("很遗憾，没有找到哦！");
}
System.out.println();
}
}
3.冒泡排序和快速排序
冒泡排序
package com.atguigu.test;
public class BubbleSortTest {
public static void main(String[] args) {
int[] array1 = new int[]{43, 32, 76, -98, 0, 64, 33, -21, 32, 99};
//冒泡排序
int test;
for(int i = 0;i < array1.length - 1;i++)
{
for(int j = 0;j < array1.length - i - 1;j++)
{
if(array1[j] > array1[j + 1])
{
test = array1[j];
array1[j] = array1[j + 1];
array1[j + 1] = test;
}
}
}
for(int i = 0;i < array1.length;i++)
{
System.out.print(array1[i] + "t");
}
}
}
快速排序
package com.atguigu.java;
public class QuickSort {
private static void swap(int[] data, int i, int j) {
int temp = data[i];
data[i] = data[j];
data[j] = temp;
}
private static void subSort(int[] data, int start, int end) {
if (start < end) {
int base = data[start];
int low = start;
int high = end + 1;
while (true) {
while (low < end && data[++low] - base <= 0)
;
while (high > start && data[--high] - base >= 0)
;
if (low < high) {
swap(data, low, high);
} else {
break;
}
}
swap(data, start, high);
subSort(data, start, high - 1);//递归调用
subSort(data, high + 1, end);
}
}
public static void quickSort(int[] data){
subSort(data,0,data.length-1);
}
public static void main(String[] args) {
int[] data = { 9, -16, 30, 23, -30, -49, 25, 21, 30 };
System.out.println("排序之前：n" + java.util.Arrays.toString(data));
quickSort(data);
System.out.println("排序之后：n" + java.util.Arrays.toString(data));
}
}
4.Arrays工具类的使用
| 1 | boolean equals(int[] a,int[] b) | 判断两个数组是否相等 |
| 2 | String to String(int[], a) | 输出数组信息 |
| 3 | void fill(int[] a, int val) | 将指定值填充到数组当中 |
| 4 | void sort(int[] a) | 对数组进行排序 |
| 5 | int binarySearch(int[] a,int key) | 对排序后的数组进行二分法检索指定的值 |
package com.atguigu.test;
import java.util.Arrays;
public class ArraysTest {
public static void main(String[] args) {
//1 boolean equals(int[] a,int[] b) 判断两个数组是否相等
int[] arr1 = new int[]{1, 2, 3, 4};
int[] arr2 = new int[]{1, 3, 2, 4};
boolean isEquals = Arrays.equals(arr1, arr2);
System.out.println(isEquals);
//2 String to String(int[], a) 输出数组信息
System.out.println(Arrays.toString(arr1));
//3 void fill(int[] a, int val) 将指定值填充到数组当中
Arrays.fill(arr1, 10);
System.out.println(Arrays.toString(arr1));
//4 void sort(int[] a) 对数组进行排序
Arrays.sort(arr2);
System.out.println(Arrays.toString(arr2));
//5 int binarySearch(int[] a,int key) 对排序后的数组进行二分法检索指定的值
int[] arr3 = new int[]{-98, -34, 2, 34, 54, 66, 79, 105, 210, 333};
int index = Arrays.binarySearch(arr3, 2);
System.out.println(index);//index若返回一个负数，则没找到
}
}
5.数组中常见异常
package com.atguigu.test;
public class ArrayExceptionTest {
public static void main(String[] args) {
//1.角标越界
int[] arr = new int[]{1, 2, 3, 4, 5};
//System.out.println(arr[5]);
//System.out.println(arr[-2]);
//情况三：
String[] arr3 = new String[]{"AA","BB","CC"};
arr3[0] = null;
System.out.println(arr3.toString());//对象是null
}
}
