开发基础知识，Java对象比较和排序

一、比较对象是否相等

复写equals和hashCode方法

public class Student  {
    private String name;
    private int age;

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (!(o instanceof Student)) return false;
        Student student = (Student) o;
        return getAge() == student.getAge() && SortUtils.equals(getName(), student.getName());
    }

    @Override
    public int hashCode() {
        return SortUtils.hashCode(getName(), getAge());
    }
}


public class SortUtils {
    public static boolean equals(Object a, Object b) {
        return (a == b) || (a != null && a.equals(b));
    }

    public static int hashCode(Object ... values) {
        return Arrays.hashCode(values);
    }
}

二、List集合排序方法一

1. 实现 Comparable接口
2. 调用 Collections.sort(list)进行排序

public class Student implements Comparable<Student> {
    private String name;
    private int age;
    @Override
    public int compareTo(Student student) {
        if (student == null) {
            return 0;
        }
        // 按年龄从小到大排序
        int sort = this.age - student.age;
        if (sort == 0) {
            if (!TextUtils.isEmpty(this.name)&&!TextUtils.isEmpty(student.name)){
                sort = this.name.compareTo(student.name);
            }
        }
        return sort;
    }
}

三、List集合排序方法二

1. 自定义类，继承Comparator
2. 调用 Collections.sort(list,comparator)进行排序

public class StudentComparator implements Comparator<Student> {
    @Override
    public int compare(Student stu1, Student stu2) {
        if (stu1 == null || stu2 == null) {
            return 0;
        }
        // 按年龄从大到小排序
        int sort = stu2.getAge() - stu1.getAge();
        // 年龄一样，按姓名排序
        if (sort == 0) {
            if (!TextUtils.isEmpty(stu1.getName()) && !TextUtils.isEmpty(stu2.getName())) {
                sort = stu1.getName().compareTo(stu2.getName());
            }
        }
        return sort;
    }
}

四、综合测试代码

    protected void test() {
        Student s1 = new Student("Lven", 18);
        Student s2 = new Student("Kven", 25);
        Student s5 = new Student("Lven", 19);
        Student s6 = new Student("Lven", 19);
        Student s3 = new Student("Rven", 25);
        Student s4 = new Student("Kven", 19);

        // 优先使用构造参数进行排序
        Set<Student> set = new TreeSet<>(new StudentComparator());
        set.add(s1);
        set.add(s1);
        set.add(s2);
        set.add(s5);
        set.add(s3);
        set.add(s6);
        set.add(s4);
        // 优先使用第二个参数进行排序
        // Collections.sort(list,new StudentComparator());
        for (Student student : set) {
            Log.e("MainActivity", student.toString());
        }
    }

set排序结果.png