数组和集合

数组转集合

String[] strArray = new String[]{"aaa","bbb","ccc"};
//注意此时转出来的集合对应不是java.util.ArrayList对象,是Arrays内部的一个ArrayList对象,继承自AbstractList,该父类的add和remove方法会抛出异常
List<String> strArray2List = Arrays.asList(strArray);
//如需转换成java.util.ArrayList对象,可使用构造方法转换
List<String> strArray2List = new ArrayList(Arrays.asList(StrArray));

集合转数组

List<String> strList = new ArrayList(){{add("aaa");add("bbb");add("ccc")}};
//注意该方法会出现类型转换异常,因为ArrayList的实例对象的toArray方法返回的是一个Object[]数组,强转成String[]会转义失败
String[] strList2Array = (String[]) strList.toArray();
//上面的方法可以使用带有泛型参数的toArray方法,这样返回的结果也是泛型的对象,这样就不会有类型转换的异常了
String[] strList2Array = strList.toArray(new String[strList.size()]);

hashmap集合初始化

Map<String, String> BX_TEMPLATE_FILE = new HashMap(){
    {
        put("id","templateId");
        put("job_id", "jobId");
        put("rule_id", "ruleId");
        put("rule_desc", "ruleDesc");
        put("data_date", "dateDate");
        put("org_no", "orgNo");
        put("level", "level1");
        put("tab_name1", "tabName1");
        put("tab_name2", "tabName2");
        put("table_ch_name", "tabChName");
        put("pk_name", "pkName");
        put("col_name", "colName");
        put("上季度问题数据量", "lastQuarterProblemData");
        put("上季度数据总量", "lastQuarterData");
        put("上季度问题占比", "lastQuarterProblemPercent");
        put("本季度问题数据量", "quarterProblemData");
        put("本季度数据总量", "quarterData");
        put("本季度问题占比", "quarterProblemPercent");
        put("本季度问题数据量-上季度问题数据量", "quarterProblemAdd");
        put("（本季度问题数据量-上季度问题数据量）/上季度问题数据量", "quarterProblemAddpercent");
        put("except_sample", "exceptSample");
        put("bank_name", "bankName");
        put("机构简称", "bankShortName");
        put("importDate", "importDate");
        put("reason", "reason");
        put("reasonName", "reasonName");
        put("reasonTime", "reasonTime");
        put("dataStatus", "dataStatus");
        put("sqlRecord", "sqlRecord");
    }
};
//HASHMAP是hash散列的,如果要线性的,需要用LinkedHashMap:
Map<String, String> BX_TEMPLATE_FILE = new LinkedHashMap(){
    {
        put("id","templateId");
        put("job_id", "jobId");
        put("rule_id", "ruleId");
        put("rule_desc", "ruleDesc");
        put("data_date", "dateDate");
        put("org_no", "orgNo");
        put("level", "level1");
        put("tab_name1", "tabName1");
        put("tab_name2", "tabName2");
        put("table_ch_name", "tabChName");
        put("pk_name", "pkName");
        put("col_name", "colName");
        put("上季度问题数据量", "lastQuarterProblemData");
        put("上季度数据总量", "lastQuarterData");
        put("上季度问题占比", "lastQuarterProblemPercent");
        put("本季度问题数据量", "quarterProblemData");
        put("本季度数据总量", "quarterData");
        put("本季度问题占比", "quarterProblemPercent");
        put("本季度问题数据量-上季度问题数据量", "quarterProblemAdd");
        put("（本季度问题数据量-上季度问题数据量）/上季度问题数据量", "quarterProblemAddpercent");
        put("except_sample", "exceptSample");
        put("bank_name", "bankName");
        put("机构简称", "bankShortName");
        put("importDate", "importDate");
        put("reason", "reason");
        put("reasonName", "reasonName");
        put("reasonTime", "reasonTime");
        put("dataStatus", "dataStatus");
        put("sqlRecord", "sqlRecord");
    }
};

集合的深拷贝

/**
 * @description: 深拷贝src集合，集合对象需要实现IEntityClone接口
 * @params: [src]
 * @return: java.util.Collection<T>
 * @date: 2023/2/20
 */
public static <T extends IEntityClone> Collection<T> copyOf(Collection<T> src) throws InstantiationException, IllegalAccessException{
    Collection target = src.getClass().newInstance();
    src.stream().forEach(t->target.add(t.clone()));
    return target;
}

public interface IEntityClone extends Cloneable{

    default IEntityClone clone() {
        return null;
    }
}

使用示例

package pers.xiaotian.entity;

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
import pers.xiaotian.utils.IEntityClone;

@Data
@AllArgsConstructor
@NoArgsConstructor
public class Person implements IEntityClone {
    private int age;
    private String name;
    private Job job;

    @Override
    public Person clone(){
        return new Person(this.age, this.name, job.clone());
    }
}

package pers.xiaotian.entity;

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
import pers.xiaotian.utils.IEntityClone;

@Data
@AllArgsConstructor
@NoArgsConstructor
public class Job implements IEntityClone {
    private String title;

    @Override
    public Job clone(){
        return new Job(this.title);
    }
}

    @Test
    public void collectionsObjectCopyTest() throws InstantiationException, IllegalAccessException{
//        使用字面量初始化集合对象参数的方式不行!!!
//        List<Person> src = new ArrayList(){{
//            add(new Person(20, "张三", new Job("老师")));
//            add(new Person(21, "李四", new Job("医生")));
//            add(new Person(22, "王五", new Job("学生")));
//        }};
        List<Person> src1 = new ArrayList();
        src1.add(new Person(20, "张三", new Job("老师")));
        src1.add(new Person(21, "李四", new Job("医生")));
        src1.add(new Person(22, "王五", new Job("学生")));
        List<Person> dest = (List<Person>) CollectionsUtil.copyOf(src1);
        System.out.println(Arrays.toString(dest.toArray()));
        dest = new ArrayList<>(dest);
        dest.remove(0);
        dest.get(0).setAge(25);
        dest.get(0).getJob().setTitle("高级医生");
        System.out.println(Arrays.toString(dest.toArray()));
        System.out.println(Arrays.toString(src1.toArray()));
    }

测试结果:

基本类型数组转包装类型集合,已char[]和int[]为例

@Test
public void baseTypeArrToList(){
    char[] arr = new char[]{'a','b','c'};
    List<Character> list = new String(arr).chars().mapToObj(i->(char)i).collect(Collectors.toList());
    int[] arr1 = new int[]{1,2,3};
    List<Integer> list1 = Arrays.stream(arr1).boxed().collect(Collectors.toList());
    System.out.println(Arrays.toString(list.toArray()));
    System.out.println(Arrays.toString(list1.toArray()));

}

测试结果:

List set(index, element)和add(index, element)方法的使用说明.

set方法是做修改替换操作,如果当前index还不存在,会提示IndexOutOfBoundsException错误.

add方法是做新增操作,将当前element插入到index的目标位置,之前存在目标位置的index做右移.