java中的比较方法

Java中比较的方法主要有以下几类

一：==运算符

==运算符常用来比较==左右两侧是否相等，如果左右两侧是基本数据类型，比较的是值是否相等；如果==左右两侧是引用类型，比较的是引用变量的地址是否相等

public class TestDemo {
    public static void main(String[] args) {
        String a = "hsp";
        String b = "java";
        Person c = new Person("李华",20);
        Person d = new Person("李华",20);
        Person e = c;
        System.out.println(a == b);
        System.out.println(c == d);
        System.out.println(e == c);
    }
}
class Person{
    private String name;
    private int age;

    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }
}

二：equals()

equals()方法常用来比较两个对象的地址是否相同，如果要比较对象中的类容，必须重写Object中的equals方法 

public class TestDemo {
    public static void main(String[] args) {
        String a = "hsp";
        String f = "hsp";
        System.out.println(a.equals(f));//true

        Person c = new Person("李华",20);
        Person d = new Person("李华",21);
        System.out.println(c.equals(d));//false

    }
}
class Person{
    private String name;
    private int age;

    public Person(){

    }
    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }

    @Override
    public boolean equals(Object obj) {
        if(this==obj)return true;//自己和自己比
        if(!(obj instanceof Person)||obj==null)return false;//如果对象为空或者不是Person子类返回false
        Person person = (Person) obj;
        return this.name.equals(person.name)&&this.age==person.age;
    }
}

重写equals的方式虽然可以比较，但equals只能按照相等进行比较，不能按照大于、小于的方式进行比较。 

三：基于Comparable接口类的比较

方法：实现Comparable接口，重写CompareTo方法

public class TestDemo2 {
    public static void main(String[] args) {
        Student[] student = new Student[3];
        student[0] = new Student(20185427,"李华");
        student[1] = new Student(20185434,"尹朝龙");
        student[2] = new Student(20185421,"阿资曲不");
        Arrays.sort(student);
        System.out.println(Arrays.toString(student));
    }
}
class Student implements Comparable<Student>{
    private int num;
    private String name;
    public Student(int num,String name){
        this.num = num;
        this.name = name;
    }

    @Override
    public int compareTo(Student o) {
        return this.num-o.num;
    }


    @Override
    public String toString(){
        return "学号:"+num+" "+"姓名:"+name;
    }
}

四：自己定义比较器，实现Comparator接口

方法：自己定义比较器，实现Comparator接口，重写compara方法

public class TestDemo3 {
    public static void main(String[] args) {
        Student2[] student2 = new Student2[3];
        student2[0] = new Student2(20185427,"李华");
        student2[1] = new Student2(20185434,"尹朝龙");
        student2[2] = new Student2(20185421,"阿资曲不");
        Arrays.sort(student2,new StudentComparator());
        System.out.println(Arrays.toString(student2));
    }
}
class Student2{
    public int num;
    public String name;
    public Student2(int num,String name){
        this.num = num;
        this.name = name;
    }
    @Override
    public String toString(){
        return "学号:"+num+" "+"姓名:"+name;
    }
}
class StudentComparator implements Comparator<Student2> {

    @Override
    public int compare(Student2 o1, Student2 o2) {
        return o2.num-o1.num;
    }
}

也可以这样
public class TestDemo3 {
    public static void main(String[] args) {
        Student2[] student2 = new Student2[3];
        student2[0] = new Student2(20185427,"李华");
        student2[1] = new Student2(20185434,"尹朝龙");
        student2[2] = new Student2(20185421,"阿资曲不");
        Arrays.sort(student2, new Comparator<Student2>() {
            @Override
            public int compare(Student2 o1, Student2 o2) {
                return o1.num-o2.num;
            }
        });
        System.out.println(Arrays.toString(student2));
    }
}
class Student2{
    public int num;
    public String name;
    public Student2(int num,String name){
        this.num = num;
        this.name = name;
    }
    @Override
    public String toString(){
        return "学号:"+num+" "+"姓名:"+name;
    }
}