Guava相关操作

Description

(12条消息) Guava的基础功能与集合_鲲鹏飞九万里的博客-CSDN博客_guava

package com.example.jc_demo;

import cn.hutool.core.date.DateUtil;
import com.google.common.base.Preconditions;
import com.google.common.collect.ImmutableSet;
import com.google.common.collect.Ordering;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
import lombok.extern.slf4j.Slf4j;
import org.junit.jupiter.api.Test;

import java.util.*;

@Slf4j
public class GuavaTest {
    @Data
    @AllArgsConstructor
    @NoArgsConstructor
    class User {
        String name;
    }

    @Test
    public void my_Optional() {
        Optional<Integer> op = Optional.ofNullable(new Integer(123));
        log.info(op.get().toString());
    }

    @Test
    public void returnUser() {
        User u = new User();
        u = null;
        // 如果不用ofNullable会有空指针异常 用ofNullable能够在get()的时候报出空元素异常
        Optional<User> op = Optional.ofNullable(u);
        User u1 = op.get();
        log.info(u1.toString());
    }

    @Test
    public void orElse() {
        // ???防止空指针 备用值???  IFNULL???
        Optional<String> op = Optional.of("aaa");
        log.info(String.valueOf(op.isPresent()));
        log.info(op.orElse(null));
    }

    @Test
    public void isPresent() {
        Optional<String> op = Optional.of("2322");
        log.info(String.valueOf(op.isPresent()));

        Optional<String> op1 = Optional.ofNullable(null);
        log.info(String.valueOf(op1.isPresent()));
    }

    //

    @Test
    public void my_Preconditions() {
        int i = -1;
        int j = 10;
        String k = null;
        // Preconditions.checkArgument(i > j, "%s is not bigger than %s", i, j);
        // Preconditions.checkNotNull(k,"k is null");
        // Preconditions.checkArgument("1".equals("2"),"1 is not equals 2");

        // int[] arr = new int[10];
        // Preconditions.checkElementIndex(20,arr.length);
    }

    @Test
    public void myImmutableSet() {
        /**
         * 三种方式创建 只读数组
         * 1.of
         * 2.builder
         * 3.copy
         *
         * 注意：不可放入null
         */
        ImmutableSet<String> immutableSet = ImmutableSet.of("a", "b", "c");
        immutableSet.forEach(e->{
            log.info(e);
        });
        // java.lang.UnsupportedOperationException 不允许操作数组， 只读
        // immutableSet.add("d");

        ImmutableSet<String> immutableSet1 = ImmutableSet.<String>builder()
                .add("a")
                .add("b")
                .add("c")
                .build();

        immutableSet1.forEach(e->{
            log.info(e);
        });
        // java.lang.UnsupportedOperationException 不允许操作数组， 只读
        // immutableSet1.add("d");

        // ImmutableSet<String> immutableSet3 = ImmutableSet.copyOf(arrayList);

    }

    @Data
    @AllArgsConstructor
    @NoArgsConstructor
    private class Device {
        Date CreatTime;
        Date UpdateTime;
    }

    @Test
    public void my_Order() {
        Ordering ordering = new Ordering<String>() {
            // order by length
            @Override
            public int compare(String s, String t1) {
                return s.length() > t1.length() ? new Integer(1) : new Integer(-1);
            }
        };

        ArrayList<String> list = new ArrayList<>();
        list.add("sadewf");
        list.add("sadewfsda");
        list.add("sadewfsdaasdfeao");
        list.add("aadewfsdaasdfea");
        list.add("zoad");
        list.add("zoadnas");
        list.add("doadn");
        list.add("doadnsadasda");
        list.add("zoadnasodnaosndaosd");

        //ascii ?
        Collections.sort(list);
        My_ForEach(list);

        Collections.sort(list, ordering);
        My_ForEach(list);

        Collections.reverse(list);
        My_ForEach(list);

    }

    @Test
    public void order2() {
        // 链式调用  从右往左调用，先orderBy XXX 将Null放最前或最后   对剩下的自然排序
        Ordering<Device> ordering1 = Ordering.natural().nullsFirst().onResultOf((Device device) -> device.CreatTime);
        Ordering<Device> ordering2 = Ordering.natural().nullsLast().onResultOf((Device device) -> device.CreatTime);
        List<Device> list1 = new ArrayList<>();
        list1.add(new Device(DateUtil.parse("2022-1-1", "yyyy-MM-dd"), null));
        list1.add(new Device(null, null));
        list1.add(new Device(DateUtil.parse("2022-1-8", "yyyy-MM-dd"), null));
        list1.add(new Device(DateUtil.parse("2021-1-7", "yyyy-MM-dd"), null));
        list1.add(new Device(DateUtil.parse("2022-5-1", "yyyy-MM-dd"), null));
        list1.add(new Device(DateUtil.parse("2022-1-7", "yyyy-MM-dd"), null));
        list1.add(new Device(DateUtil.parse("2022-3-1", "yyyy-MM-dd"), null));
        list1.add(new Device(DateUtil.parse("2022-6-1", "yyyy-MM-dd"), null));

        Collections.sort(list1, ordering2);

        My_ForEach(list1);
    }

    @Test
    public void isOrder() {
        List<String> list = new ArrayList<>(Arrays.asList("a", "asd", "b", "asdve"));

        // 返回降序前两个
        List<String> list1 = Ordering.natural().greatestOf(list, 2);
        // 返回升序后两个
        List<String> list2 = Ordering.natural().leastOf(list, 2);

        My_ForEach(list1);
        My_ForEach(list2);
    }

    public void My_ForEach(List list) {
        if (list.size() > 0) {
            list.forEach(e -> {
                log.info(e.toString());
            });
        } else {
            log.error("空集合");
        }
        log.info("=======================================================");
    }
}