Java Foundation 03-12_ Object Comparison

Object comparison

If you now have two numbers to determine whether they are equal, you can use "= =" to complete

If the string is to be judged for equality use "equals ()"

But if there is a custom class Now, to determine whether its two objects are equal, then it is necessary to implement a comparison of all the property contents within the Class object.

Example: How the underlying comparison works

class Book {    private String title;    private double price;    public Book(String title, double price) {        this.title = title;        this.price = price;    }    public String getTitle() {        return this.title;    }    public double getPrice() {        return this.price;    }}public class TestDemo {    public static void main(String args[]) {        Book b1 = new Book("Java开发", 79.8);// 实例化Book类对象        Book b2 = new Book("Java开发", 79.8);// 实例化Book类对象        if (b1.getTitle().equals(b2.getTitle())&& b1.getPrice() == b2.getPrice()) // 属性比较            System.out.println("是同一个对象！");        } else {            System.out.println("不是同一个对象！");        }    }}

Example: Object comparison implementation

class Book {    private String title ;    private double price ;    public Book(String title,double price) {        this.title = title ;        this.price = price ;    }    /**     * 进行本类对象的比较操作，在比较过程中首先会判断传入的对象是否为null，而后判断地址是否相同，     * 如果都不相同则进行对象内容的判断，由于compare()方法接收了本类引用，所以可以直接访问私有属性     * @param book 要进行判断的数据     * @return 内存地址相同、或者属性完全相同返回true，否则返回false     */    public boolean compare(Book book) {        if (book == null) {     // 传入数据为null            return false ;      // 没有必要进行具体的判断        }        // 执行“b1.compare(b2)”代码时会有两个对象：当前对象this（调用方法对象，就是b1引用）； 传递的对象book（引用传递，就是b2引用）        if (this == book) {     // 内存地址相同            return true ;       // 避免进行具体细节的比较，节约时间        }        if (this.title.equals(book.title)            && this.price == book.price) {  // 属性判断            return true ;        } else {    return false ;  }    }// setter、getter略}

Java Foundation 03-12_ Object Comparison