Java小练习

Generic接口

public interface Generic<T> {
    void get(T t);
}

Generic接口实现

public class GenericImpl<T> implements Generic<T>{
    @Override
    public void get(T t) {
        System.out.println("这里是GenericImpl,t的值为：[" + t + "]");
    }
}

实体类

import lombok.Data;

@Data
public class Info {
    private String name;
    private int num;
    private int price;
}

测试类

public class Test {
    public static void main(String[] args) {
        System.out.println("====================");
        //运算符问题
        int i1 = 10;
        int i2 = 10;
        System.out.println("i" + i1 + i2);
        //System.out.println("i"+i1-i2); 报错！！！
        System.out.println("i" + i1 * i2);
        System.out.println("i" + i1 / i2);
        System.out.println("====================");
        //运算符优先级问题
        int k = 0;
        int g = 0;
        int ret1 = ++k + k++ + ++k + k;
        int ret2 = ++g + g++ + g++ + g;
        System.out.println(ret1);
        //1+1+3+3
        //k++自身不变，运算完后才加1 如果后面是++k 那麽就1+ ++k
        System.out.println(ret2);
        //1+1+2+3
        System.out.println("====================");
        //递归阶乘
        for (int n = 1; n <= 5; n++) {
            int ret3 = recursive(n);
            System.out.println(n + "的阶乘值：" + ret3);
        }
        System.out.println("====================");
        //删除字符串"evwevwea-531g4j31"里的数字
        String str = "evwevwea-531g4j.31";
        String result = str.replaceAll("\\d", "");
        System.out.println(result);
        System.out.println("====================");
        //调用泛型接口
        GenericImpl<DmArea> generic = new GenericImpl<>();
        generic.get(new DmArea());
        System.out.println("====================");
        //集合装对象转Json
        Info info1 = new Info();
        Info info2 = new Info();
        Info info3 = new Info();
        List<Info> infoList = new ArrayList<>();
        info1.setName("a");
        info1.setNum(253);
        info1.setPrice(256);
        infoList.add(info1);
        info2.setName("b");
        info2.setNum(125);
        info2.setPrice(852);
        infoList.add(info2);
        info3.setName("c");
        info3.setNum(23);
        info3.setPrice(78);
        infoList.add(info3);
        String jsonString = JSON.toJSONString(infoList);
        System.out.println(jsonString);
    }

    private static int recursive(int n) {
        if (n < 1) {
            return 1;
        }
        //递归出来的结果（核心）
        return recursive(n - 1) * n;
    }
}