2.java数组，类

浅浅的花香味﹌ 2024-04-01 19:21 74阅读 0赞

**数组**

![12b4f87a06254361ad78cec463a93e6a.png][]

![c9d3b8a9a20b449d89aa2f3c10e1555d.png][]

![cf6d6da6adff4758b2b0859860a605c1.png][]

//静态初始化
        int[][] a={
       {1,2,3,4},{4,5,6,7},{8,9,10,11}};
        //动态初始化
        String[][] b=new String[10][10];
        b[0]=new String[]{"zahngsan","lisi","wangwu"};
        b[1]=new String[]{"java","python","c++"};

**类与对象**

![15cd2ebdfa48483aad89a1f6b8c76f83.png][]

![4074f3ae2cb948e1acf8b5baf7d4aae7.png][]

**属性**

public class Test1 {
        public static void main(String[] args) {
            Cat cat = new Cat();
        }
    }
    class Cat{
        String name;
        int age;
        String color;
        double weight;
    }

![d82e9fdb4bfb40329e28213365dd38a2.png][]

类信息只会加载一次

![9dcd49388a45480aaf7618aa1bd68839.png][]

![9d8af1cbe2494cdaaa11c823f54f8cd9.png][]

**方法**

public class Test1 {
        public static void main(String[] args) {
            Cat cat = new Cat();
            cat.run();
        }
    }
    class Cat{
        public void run(){
            System.out.println("跑");
        }
    }

![0d0ed69507fc4b4e8d9c4018dc43be9f.png][]

![ba60bc4af9454f4d95db5f332739dbf5.png][]

**小练习**

编写一个类，里面来一个判断是否是偶数的。在main里面调用

**方法传参**

**基本数据类型**

基本数据拷贝，传值

public static void main(String[] args) {
            int a = 10;
            int b = 20;
            Cat cat = new Cat();
            cat.swap(a,b);
            System.out.println("main方法a="+a+"b="+b);
        }
    }
    class Cat{
        public void swap(int a,int b){
            System.out.println("a="+a+"b="+b);
            int tmp = a;
            a = b;
            b = tmp;
            System.out.println("a="+a+"b="+b);
        }
    }

![4fb4234c773c4401b1079cec47bf2cb0.png][]

**引用数据类型**

引用数据类型，**地址值**

java中方法参数传递方式是本质上都是“值”传递

如果参数是基本类型（传“实际值”）：

由于栈中存的就是“实际值”（java基本类型的值存储在栈中，不在堆中），所以传递的是基本类型的“实际值”的拷贝。

如果参数是引用类型（传“地址值”）：

由于栈中存的是地址（该地址指向堆内存中存储位置，即引用），所以传递的是“堆中的地址”的拷贝。所以我们说成是“引用（址）传递”。

注意：

1.  “String和8大基本类型的包装类”是不可变类型，即特殊的引用类型，所以每次修改操作都是新创建的对象，栈中的地址不断更换，所以出现了不能修改值的效果，让大家误以为是值传递了。
2.  而一般对我们自己创建的类进行修改操作，就会顺着
3.  引用的地址“找到并修改掉”原来的值，所以达到了引用传递的效果。
4.

public class Test1 {
        public static void main(String[] args) {
            int[] a = {10,2,3};
            System.out.println(Arrays.toString(a));
            Cat cat = new Cat();
            cat.AA(a);
            System.out.println(Arrays.toString(a));
        }
    }
    class Cat{
        public void AA(int a[]){
            a[0] = 20000;
            System.out.println(Arrays.toString(a));
        }
    }

1.  ![62051097ffab4ac58e1492f79c6976a2.png][]

对象的传递

public class Test1 {
        public static void main(String[] args) {
            A a = new A();
           Dog dog1 = new Dog();
            dog1.name = "sjb";
            dog1.age = 19;
            a.aaa(dog1);
            System.out.println(dog1.age+"    "+dog1.name);
        }
    }
    class Dog {
        String name;
        int age;
    }
    class A{
        public void aaa(Dog dog){
            dog.age = -1;
        }
    }

**递归**

![66356c75c44944ab811d6756f120e02e.png][]

![651cca698fa3460dbe9fb7b8ca981f2c.png][]

![7a6d5ff932ae45779410e58eea143ac2.jpeg][]

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[c9d3b8a9a20b449d89aa2f3c10e1555d.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/01/607caf771ef24ca7b2942aed3077f65f.png
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[15cd2ebdfa48483aad89a1f6b8c76f83.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/01/c791e84d7bf84c93929de7cc33883db9.png
[4074f3ae2cb948e1acf8b5baf7d4aae7.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/01/9a29416b53ec496c89d020e21de5ec6f.png
[d82e9fdb4bfb40329e28213365dd38a2.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/01/d675a8a4ccae45d690eaf6a1393c7e2a.png
[9dcd49388a45480aaf7618aa1bd68839.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/01/83cb9be92b314d31a658a5dfe52636fe.png
[9d8af1cbe2494cdaaa11c823f54f8cd9.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/01/b03bfbdf0fc3444b837006f52caa082f.png
[0d0ed69507fc4b4e8d9c4018dc43be9f.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/01/aefbdb8faa544e01b7916a08722d8479.png
[ba60bc4af9454f4d95db5f332739dbf5.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/01/43c8550ca35a455c85702904cdd47a01.png
[4fb4234c773c4401b1079cec47bf2cb0.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/01/32b0f029b3e9490b94277766624da178.png
[62051097ffab4ac58e1492f79c6976a2.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/01/8ac8d375d55d43cd977c0c463ae8931b.png
[66356c75c44944ab811d6756f120e02e.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/01/873b622a51ac4adf8295c0b2b70dabc9.png
[651cca698fa3460dbe9fb7b8ca981f2c.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/01/2875a7c02c2b4e0a8bfef6252210632b.png
[7a6d5ff932ae45779410e58eea143ac2.jpeg]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/01/42f197137ccc4eeebb55de396ed84a49.jpeg