1、相等性的比較
1）原生數(shù)據(jù)：值
2）引用類型：指向同一地址/引用地址

2、java.lang.Object類
java.lang包使用時(shí)無(wú)需顯式導(dǎo)入

3、API:Application Programming Interface

4、打印引用時(shí)，打印的是引用所指對(duì)象的toString()方法的返回值。因?yàn)槊總€(gè)類都直接或間接地繼承自O(shè)bject，而Object類中定義了toString()，因此每個(gè)類都有toString()這個(gè)方法。

public class ObjectTest
{
    public static void main(String[] args)
    {
        Object object = new Object();

        System.out.println(object);
        System.out.println(object.toString());

        String str = "aaa";

        System.out.println(str);
        System.out.println(str.toString());

        Student student = new Student();

        System.out.println(student);
        System.out.println(student.toString());

    }
}

class Student extends Object
{
    public String toString()
    {
        return "Hello World";
    }
}

5、關(guān)于進(jìn)制：
十六進(jìn)制用 0-9 a、b、c、d、e、f 表示
例：十六進(jìn)制的123 轉(zhuǎn)化為十進(jìn)制 即為：116^2+216^1+3*160

6、

public class ObjectTest2
{
    public static void main(String[] args)
    {
        Object object = new Object();
        Object object2 = new Object();

        System.out.println(object == object2);//false

        System.out.println("---------------");

        String str = new String("aaa");
        String str2 = new String("aaa");

        System.out.println(str == str2);//false

        System.out.println("---------------");

        String str3 = "bbb";
        String str4 = "bbb";

        System.out.println(str3 == str4);//true

        System.out.println("---------------");

        String str5 = new String("ccc");
        String str6 = "ccc";

        System.out.println(str5 == str6);//false

        System.out.println("---------------");

        String s = "hello";
        String s1 = "hel";
        String s2 = "lo";

        System.out.println(s == s1 + s2);//false

        System.out.println("---------------");

        System.out.println(s == "heo" + "lo");//true

    }
}