由equal和==引发的问题

Student student1 = new Student();
Student student2 = new Student();
System.out.println(student1.equals(student2));//false
System.out.println(student1 == student2);//false

String a = new String("a");
String b = new String("a");
System.out.println(a == b);//false
System.out.println(a.equals(b));//true
System.out.println(student1.toString().equals(student2.toString()));//false


String a = new String("aw");
String b = new String("aw");
System.out.println(a==b);//false
String a = new String("aw");
String b = new String("aw");
String c= "aa";
String d= "aa";
System.out.println(a==b);//false
System.out.println(c==d);//true