Some finishing questions about the Beginner Java interview (partially transferred from others)

1. What are the aspects of object-oriented features
1. Abstraction:
Abstraction is about ignoring aspects of a topic that are not related to the current goal, so that you can more fully focus on the aspects that are relevant to the current goal. Abstractions do not intend to understand all of the problems, but simply select one part of them, temporarily without some detail. Abstract includes two aspects, one is the process abstraction, the other is the data abstraction.
2. Inheritance:
Inheritance is a hierarchical model of a junction class and allows and encourages the reuse of classes, which provides a way to articulate commonalities. A new class of objects can be derived from existing classes, a process known as class inheritance. The new class inherits the attributes of the original class, which is called the derived class (subclass) of the original class, and the original class is called the base class of the new class (The parent Class). Derived classes can inherit methods and instance variables from their base classes, and classes can modify or add new methods to make them more suitable for special needs.
3. Package:
Encapsulation is the process and data is surrounded, access to data only through the defined interface. Object-oriented computing begins with this basic concept that the real world can be portrayed as a series of fully autonomous, encapsulated objects that access other objects through a protected interface.
4. Polymorphism:
Polymorphism refers to allowing objects of different classes to respond to the same message. Polymorphism consists of parameterized polymorphism and inclusion polymorphism. Polymorphism language has the advantage of flexibility, abstraction, behavior sharing and code sharing, which solves the problem of application function with the same name.
2. Is string the most basic data type?
The basic data types are byte, int, char, long, float, double, Boolean, and short.
The Java.lang.String class is of the final type, so you cannot inherit the class or modify the class. To improve efficiency and save space, we should use the StringBuffer class.

3. What is the difference between int and Integer
Java offers two different types: reference types and primitive types (or built-in types). int is the raw data type of Java, and integer is the wrapper class provided by Java for Int. Java provides a wrapper class for each primitive type.
Raw type Encapsulation class
Booleanboolean
Charcharacter
Bytebyte
Shortshort
Intinteger
Longlong
Floatfloat
Doubledouble
The behavior of reference types and primitive types is completely different, and they have different semantics. Reference types and primitive types have different characteristics and usages, including: size and speed issues, which types of data structures are stored as the default values that are specified when reference types and primitive types are used as instance data for a class. The default value of an object reference instance variable is NULL, and the default value of the original type instance variable is related to their type.
4. The difference between String and StringBuffer
The Java platform provides two classes: string and StringBuffer, which can store and manipulate strings, which are character data that contain multiple characters. This string class provides a string of values that cannot be changed. The string provided by this StringBuffer class is modified. You can use StringBuffer when you know that character data is going to change. Typically, you can use Stringbuffers to dynamically construct character data.
5. What are the similarities and differences between abnormal operation and general anomaly?
An exception represents an unhealthy state that may occur during a program's run, and a run-time exception that represents an exception that may be encountered in a typical operation of a virtual machine is a common run error. The Java compiler requires the method to declare a non-runtime exception that might occur, but does not require that a runtime exception that is not caught to be thrown must be declared.

Some finishing questions about the Beginner Java interview (partially transferred from others)