idea工具控制台输出行数有

最近有个同学说入参50万数据，出参10万不相同的随机数。怎么实现？

结果查看，控制台显示不全，于是调大就好了。

复制到vscode中查找哪些重复了：

代码想到两种写法，

package sample.entity;

import java.util.ArrayList;
import java.util.List;
import java.util.Random;

public class  TestListNumber {
    public static void main(String[] args) {
//        long start = System.currentTimeMillis();
//        List<Integer> lists = TestListNumber.getNumber(500000);
//        long end = System.currentTimeMillis();
//        System.out.println(lists.size()+"---"+(end-start)+"ms");

        long start = System.currentTimeMillis();
        Integer[] a = TestListNumber.getNumber2(500000);
        long end = System.currentTimeMillis();
        System.out.println("结果："+a.length+"---"+(end-start)+"ms");
//        for (int i = 0; i < a.length; i++) {
//            System.out.println(a[i]);
//        }

    }
    static Random r = new Random();

    public static List<Integer> getNumber(int num){
        List<Integer> out = new ArrayList<>();
        int i=1;
        int j=0;
        while (i<=100000){
            j = r.nextInt(num);
            if(out.contains(j)){
                continue;
            }
            out.add(j);
            i++;
        }
        return out;
    }
    public static Integer[] getNumber2(int num){
        Integer out[] = new Integer[100000];
        int i=0;
        int j=0;
        out:while (i<100000){
            j = r.nextInt(num);
            out[i]=j;
            //System.out.println((i+1)+"----"+out[i]);
            for (int k = 0; k < i; k++) {
                if (out[k] == out[i]) {
                    //System.out.println("重复----"+out[i]);
                    continue out;
                }
            }
            i++;
        }
        return out;
    }
}

明显，数组效率好。看还有什么更好的实现呢。

Java8新式写法

  //粘贴一个java8的stream()串行写法，parallelStream()并行写法和传统for写法的处理时间对比
    @Test
    public void contextLoads() {
        //初始化一个list
        long first = new Date().getTime();
        List<Student> list = new ArrayList<>();
        for (int i = 1; i < 5000; i++) {
            Student listToMap = new Student();
            listToMap.setId(i);
            listToMap.setName("name" + i);
            listToMap.setAge(i + 20);
            list.add(listToMap);
            try {
                Thread.sleep(1);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        System.out.println("传统所用时间" + (new Date().getTime() - first));
        long startTime = new Date().getTime();
        list.stream().forEach(f -> {
            try {
                Thread.sleep(1);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        });
        System.out.println("串行所用时间" + (new Date().getTime() - startTime));


        long endTime = new Date().getTime();
        list.parallelStream().forEach(f -> {
            try {
                Thread.sleep(1);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        });
        System.out.println("并行所用时间" + (new Date().getTime() - endTime));
    }
}

class Student {
    private Integer id;
    private String name;
    private Integer age;

    public Student() {
    }

    public Integer getId() {
        return id;
    }

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

    public String getName() {
        return name;
    }

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

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }
}