目录

1.数据准备

2.对象数组的排序

1.实现Comparable类

2.实现Comparator类

3.匿名Comparator

3.数组常用Stream（jdk1.8）

1.数据准备

People类

public class People {

    private String name;
    private String sex;
    private Integer age;

    public People(String name, String sex, Integer age) {
        this.name = name;
        this.sex = sex;
        this.age = age;
    }
    public People() {
    }

    public String getName() {
        return name;
    }

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

    public String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }

    public Integer getAge() {
        return age;
    }

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

    @Override
    public String toString() {
        return "People{" +
                "name='" + name + ''' +
                ", sex='" + sex + ''' +
                ", age=" + age +
                '}';
    }

}

List list = new ArrayList<>();
list.add(new People("张三","男",21));
list.add(new People("李四","女",23));
list.add(new People("王五","男",26));
list.add(new People("赵六","女",21));

2.对象数组的排序

1.实现Comparable类

主要是使用Comparable类，实现其中的compareTo方法进行数据比较

在People类中实现Comparable

public class People implements Comparable

此时会要求实现compareTo方法

@Override
    public int compareTo(People o) {
        if(o.getAge()>this.getAge()){
            return 1;
        }else if(o.getAge() == this.getAge()){
            return 0;
        }else {
            return -1;
        }
    }

List list = new ArrayList<>();
list.add(new People("张三","男",21));
list.add(new People("李四","女",23));
list.add(new People("王五","男",26));
list.add(new People("赵六","女",21));

Collections.sort(list);

上边是按年龄降序进行排序，返回值一共有三种情况，大于0，小于0，等于0这三种。

若想要按年龄降序，可以把返回值1和-1的位置进行调换，或把判断条件的大于号改成小于号。

2.实现Comparator类

在People类中实现Comparator

public class People implements Comparator 

此时会要求实现compare方法

@Override
    public int compare(People o1, People o2) {
        if(o1.getAge()>o2.getAge()){
            return 1;
        }else if(o1.getAge() == o2.getAge()){
            return 0;
        }else {
            return -1;
        }
    }

List list = new ArrayList<>();
list.add(new People("张三","男",21));
list.add(new People("李四","女",23));
list.add(new People("王五","男",26));
list.add(new People("赵六","女",21));
Collections.sort(list,new People());

3.匿名Comparator

List list = new ArrayList<>();
list.add(new People("张三","男",21));
list.add(new People("李四","女",23));
list.add(new People("王五","男",26));
list.add(new People("赵六","女",21));
Collections.sort(list,new Comparator(){
            @Override
            public int compare(People o1, People o2) {
                if(o1.getAge()>o2.getAge()){
                    return 1;
                }else if(o1.getAge() == o2.getAge()){
                    return 0;
                }else {
                    return -1;
                }
            }
});

3.数组常用Stream（jdk1.8） 数组过滤

list = list.stream().filter((item)->item.getAge()>22).collect(Collectors.toList());

过滤年龄大于22。

数组值存在判断

boolean flag = list.stream().anyMatch((item)->item.getAge()==26);

数组中若存在age值为26时，返回true，若没有返回false

数组值全匹配判断

boolean flag = list.stream().allMatch((item)->item.getAge()>0);

数组中的age值都大于0时返回true，否则返回false

去重

list = list.stream().distinct().collect(Collectors.toList());

若是对象数组，需要重写对象中的equals和Hashcode方法；

持续更新，欢迎指正。