Java中array类对象 java中的array

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云端创新者 2023-06-05 09:34:33

文章标签 java 数据结构 jvm intellij-idea 算法 文章分类 Java 后端开发

第四章数组Array

数组（Array）是有序的元素序列。若将有限个类型相同的变量的集合命名，那么这个名称为数组名。组成数组的各个变量称为数组的分量，也称为数组的元素，有时也称为下标变量/12713827)。用于区分数组的各个元素的数字编号称为下标。数组是在程序设计中，为了处理方便，把具有相同类型的若干元素按有序的形式组织起来的一种形式。这些有序排列的同类数据元素的集合称为数组。

数组是用于储存多个相同类型数据的集合。数组是对象类型（引用类型）

数组是固定长度，下标是从0开始，结束下标是，length属性-1，下标不存在系统会抛出异常。

4.1 声明数组对象

声明数组，是一个有序元素集合。java中数组元素的个数是固定的（声明后不能增加元素，不能删除元素）

类型[] 变量名 = new 类型[];

/声明数组，是一个有序元素集合。java中数组元素的个数是固定的（声明后不能增加元素，不能删除元素）

//声明数组，自动初始化，元素的个数是 3个下标是从0开始到 0 1 2
int[] a1 = new int[3];
var a2 = new int[3];

//声明数组并直接赋值
int[] a3 = {10, 20, 30};
int a4[] = new int[]{1, 2, 3, 4, 5};

//声明字符串数组，并直接赋值，元素个数5个 下标是0-4
String[] sts = new String[]{"李四", "王五", "张三"};

byte[] b1 = new byte[3];
short[] s1 = new short[3];
long[] lon1 = new long[]{1, 2, 3};
boolean[] bool1 = new boolean[5];
double[] d1 = new double[5];
Date[] ds = new Date[6];
char[] cs = "hello".toCharArray();
char[] c2 = new char[]{'a', 'c', 'd'};

//判断变量a2 是不是int数组
System.out.println(a2 instanceof int[]);

4.2 使用数组

数组初始化、数组赋值、读取值

数组对象有.length 属性返回数组元素的个数千万不写length()

遍历数组

package cn.yuan;
import java.util.Arrays;
public class Arr01 {
    public static void main(String[] args) {
        var ss = "java,html,css,javascript,mysql,vue,python".split(",");
        System.out.println(ss.length);
        System.out.println(ss);//输出地址
        System.out.println(Arrays.toString(ss));//以数组格式输出
        for (String s : ss) {//foreach 遍历数组
            System.out.println(s);
            //System.out.println(ss[index++]);
        }
    }
}
运行结果：
7
[Ljava.lang.String;@3b07d329
[java, html, css, javascript, mysql, vue, python]
java
html
css
javascript
mysql
vue
python

4.3 数组排序

数组排升序数组排降序数组洗牌

冒泡排序算法、洗牌算法

package cn.yuan;
import java.util.Arrays;
import java.util.Random;
public class Arr02 {
    public static void main(String[] args) {
        //声明十个元素的int数组，并赋值10个数（1-100）随机数，直接遍历输出，排序后，在输出
        Random random = new Random();
        int[] num = new int[10];
        for (int i = 1; i < num.length; i++) num[i] = random.nextInt(1, 101);
        System.out.println(Arrays.toString(num));

        //冒泡排序
        for (int a = 0; a < num.length; a++) {
            for (int b = 0; b < num.length - a - 1; b++) {
                if (num[b] > num[b + 1]) {//>升序 <降序 Math.random()>.5 乱序
                    int t;
                    t = num[b];
                    num[b] = num[b + 1];
                    num[b + 1] = t;
                }
            }
            //System.out.println(Arrays.toString(num));
        }
        System.out.println(Arrays.toString(num));
    }
}
运行结果：
[0, 77, 80, 93, 68, 64, 64, 70, 55, 38]
[0, 38, 55, 64, 64, 68, 70, 77, 80, 93]
    
洗牌算法：
package cn.yuan;
import java.util.Arrays;
import java.util.Random;
public class Arr02 {
    public static void main(String[] args) {
        //声明十个元素的int数组，并赋值10个数（1-100）随机数，直接遍历输出，排序后，在输出
        Random random = new Random();
        int[] num = new int[10];
        for (int i = 1; i < num.length; i++) num[i] = random.nextInt(1, 101);
        System.out.println(Arrays.toString(num));
     for (int i = 0; i < num.length * 2; i++) {
            int x = random.nextInt(num.length);
            int y = random.nextInt(num.length);
            if (x == y) {
                --i;
                continue;
            } else {
                int t = num[x];
                num[x] = num[y];
                num[y] = t;
            }     
        }
        System.out.println(Arrays.toString(num));
    }
}
运行结果：
[0, 26, 98, 30, 84, 91, 28, 66, 99, 8]
[30, 26, 66, 99, 84, 8, 91, 28, 0, 98]

Arrays.sort()

package cn.yuan;
public class Student implements Comparable<Student> {
    private int id;
    private String name;
    private int score;
    private String address;
    @Override
    public String toString() {
        return "Student{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", score=" + score +
                ", address='" + address + '\'' +
                '}';
    }
    public Student() {
    }
    public Student(int id, String name, int score, String address) {
        this.id = id;
        this.name = name;
        this.score = score;
        this.address = address;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getScore() {
        return score;
    }

    public void setScore(int score) {
        this.score = score;
    }

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }


    @Override
    public int compareTo(Student o) {
        //通过id和address排序
        //return id - o.id;
        return address.compareTo(o.address);
    }
}


测试类：
package cn.yuan;
import java.util.Arrays;
import java.util.Random;

public class ArrSort1 {
    public static void main(String[] args) {
        Student student = new Student();
        student.setId(10);
        student.setName("奈何");
        student.setScore(90);
        student.setAddress("新乡");
        System.out.println(student);

        Student[] stus = new Student[]{
                new Student(99, "张一", 80, "郑州"),
                new Student(2, "张二", 90, "洛阳"),
                new Student(3, "张三", 89, "郑州"),
                new Student(4, "张四", 62, "北京"),
                new Student(5, "张五", 45, "上海"),
                new Student(6, "张六", 79, "苏州")
        };
        System.out.println(Arrays.toString(stus));
        System.out.println("----------------------------------------------------------------");

        //根据对象的成绩降序
        Arrays.sort(stus, (a, b) -> b.getScore() - a.getScore());
        System.out.println(Arrays.toString(stus));
        System.out.println("----------------------------------------------------------------");
        //根据id排序
        Arrays.sort(stus);
        System.out.println(Arrays.toString(stus));
        System.out.println("----------------------------------------------------------------");

        //System.exit(0);
        //字符串排序
        String[] ss = {"java", "c", "c++", "rust", "ruby", "python", "c#"};
        System.out.println("排序前：" + Arrays.toString(ss));
        Arrays.sort(ss);
        System.out.println("升序：" + Arrays.toString(ss));
        Arrays.sort(ss, (a, b) -> b.compareTo(a));
        System.out.println("降序：" + Arrays.toString(ss));
        //根据字符长度升序
        Arrays.sort(ss, (a, b) -> a.length() - b.length());
        System.out.println("字符长度升序升序：" + Arrays.toString(ss));
        //根据字符长度降序
        Arrays.sort(ss, (a, b) -> b.length() - a.length());
        System.out.println("字符长度升序降序：" + Arrays.toString(ss));
        //洗牌
        Random random = new Random();
        for (int i = 0; i < ss.length * 5; i++) {
            int a = random.nextInt(ss.length);
            int b = random.nextInt(ss.length);
            if (a == b) {
                --i;
                continue;
            } else {
                String t = ss[a];
                ss[a] = ss[b];
                ss[b] = t;
            }
        }
        System.out.println("洗牌：" + Arrays.toString(ss));
        //数字
        Integer[] n1 = {1, 3, 0, 6, 8, 4, 2};//对象类型，基本类型报错
        System.out.println("排序前：" + Arrays.toString(n1));

        // Object[] objects = new Object[]{1, 5, new Date(), LocalDate.now()};//object是几乎所有对象的父类，万能数组

        //Arrays.sort(n1);
        Arrays.sort(n1, (x, y) -> x - y);
        System.out.println("升序：" + Arrays.toString(n1));

        Arrays.sort(n1, (x, y) -> y - x);
        System.out.println("降序：" + Arrays.toString(n1));
    }
}
运行结果：
Student{id=10, name='奈何', score=90, address='新乡'}
[Student{id=99, name='张一', score=80, address='郑州'}, Student{id=2, name='张二', score=90, address='洛阳'}, Student{id=3, name='张三', score=89, address='郑州'}, Student{id=4, name='张四', score=62, address='北京'}, Student{id=5, name='张五', score=45, address='上海'}, Student{id=6, name='张六', score=79, address='苏州'}]
----------------------------------------------------------------
[Student{id=2, name='张二', score=90, address='洛阳'}, Student{id=3, name='张三', score=89, address='郑州'}, Student{id=99, name='张一', score=80, address='郑州'}, Student{id=6, name='张六', score=79, address='苏州'}, Student{id=4, name='张四', score=62, address='北京'}, Student{id=5, name='张五', score=45, address='上海'}]
----------------------------------------------------------------
[Student{id=5, name='张五', score=45, address='上海'}, Student{id=4, name='张四', score=62, address='北京'}, Student{id=2, name='张二', score=90, address='洛阳'}, Student{id=6, name='张六', score=79, address='苏州'}, Student{id=3, name='张三', score=89, address='郑州'}, Student{id=99, name='张一', score=80, address='郑州'}]
----------------------------------------------------------------
排序前：[java, c, c++, rust, ruby, python, c#]
升序：[c, c#, c++, java, python, ruby, rust]
降序：[rust, ruby, python, java, c++, c#, c]
字符长度升序升序：[c, c#, c++, rust, ruby, java, python]
字符长度升序降序：[python, rust, ruby, java, c++, c#, c]
洗牌：[python, c#, rust, c, java, c++, ruby]
排序前：[1, 3, 0, 6, 8, 4, 2]
升序：[0, 1, 2, 3, 4, 6, 8]
降序：[8, 6, 4, 3, 2, 1, 0]

4.4 多维数组

package cn.yuan;
import java.util.Arrays;
public class Arrs01 {
    public static void main(String[] args) {
        //一二三维数组
        String[] s1;
        String[][] s2;
        String[][][] s3;
          //初始化和遍历数组
        int[][] i1 = {{1, 2, 3}, {2, 3}, {3}};
        var i2 = new int[][]{{1, 2, 3}, {2}, {3, 5}};
        System.out.println(i1[2][0]);
        System.out.println(i2[0][2]);
        for (int[] nn : i2) {
            for (int tt : nn) {
                System.out.print(tt + " ");
            }
        }
                System.out.println();
        //遍历
        System.out.println("---------------------------------");
        for (int i = 0; i < i2.length; i++) {
            for (int j = 0; j < i2[i].length; j++) {
                System.out.printf("i2[%d] [%d]= %d%n", i, j, i2[i][j]);
            }
        }
        int[][] n2 = new int[3][5];
        System.out.println(Arrays.toString(n2));//输出地址
        System.out.println(Arrays.deepToString(n2));
        System.out.println(Arrays.deepToString(i2));

        String[][][] ss3 = new String[][][]{{{"a", "b"}, {"e", "r"}, {"d", "s"}}};
        System.out.println(Arrays.deepToString(ss3));
    }
}
运行结果：
3
3
1 2 3 2 3 5 
---------------------------------
i2[0] [0]= 1
i2[0] [1]= 2
i2[0] [2]= 3
i2[1] [0]= 2
i2[2] [0]= 3
i2[2] [1]= 5
[[I@312b1dae, [I@7530d0a, [I@27bc2616]
[[0, 0, 0, 0, 0], [0, 0, 0, 0, 0], [0, 0, 0, 0, 0]]
[[1, 2, 3], [2], [3, 5]]
[[[a, b], [e, r], [d, s]]]

4.5 数组工具类

Arrays.fill()、Arrays.toString()、Arrays.sort()、Arrays.deepToString(nums)

package cn.yuan;

import java.util.Arrays;
import java.util.List;

public class Arr {
    public static void main(String[] args) {
        Integer[] n1 = {1, 2, 3};
        System.out.println(n1);//输出地址
        //数组转换为List
        List<Integer> ints = Arrays.asList(n1);
        System.out.println(ints);

        //asList（）返回List
        List<Integer> list = Arrays.asList(1, 2, 4);
        System.out.println(list);

        int[] nn = new int[6];
        System.out.println(Arrays.toString(nn));
        //数组填充值
        Arrays.fill(nn, 6);
        //从1-3 不包括3的位置填充5
        Arrays.fill(nn, 1, 3, 5);
        System.out.println(Arrays.toString(nn));
        //stream
        int sum = 0;
        for (int i : nn
        ) {
            sum += i;
        }
        System.out.println(sum);
        int sum2 = Arrays.stream(nn).sum();
        System.out.println(sum2);
        //Arrays.deepToString()
        String[][][] ss3 = new String[][][]{{{"a", "b"}, {"e", "r"}, {"d", "s"}}};
        System.out.println(Arrays.deepToString(ss3));
        //Arrays.toString()、Arrays.sort()
        String[] ss = {"java", "c", "c++", "rust", "ruby", "python", "c#"};
        System.out.println("排序前：" + Arrays.toString(ss));
        Arrays.sort(ss);
        System.out.println("升序：" + Arrays.toString(ss));
        Arrays.sort(ss, (a, b) -> b.compareTo(a));
        System.out.println("降序：" + Arrays.toString(ss));

    }
}
运行结果：
[Ljava.lang.Integer;@3b07d329
[1, 2, 3]
[1, 2, 4]
[0, 0, 0, 0, 0, 0]
[6, 5, 5, 6, 6, 6]
34
34
[[[a, b], [e, r], [d, s]]]  
排序前：[java, c, c++, rust, ruby, python, c#]
升序：[c, c#, c++, java, python, ruby, rust]
降序：[rust, ruby, python, java, c++, c#, c]

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