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How to implement polymorphism in java

The ways to achieve polymorphism in Java are: 1. Implement polymorphism through interfaces; 2. Implement polymorphism by inheriting parent classes and overriding methods; 3. Implement polymorphism by overloading methods in the same class.

Nov 11, 2019 pm 03:23 PM

java实现多态方式

The difference between equals and == in java

The differences between equals and == in Java are: 1. == compares whether two references point to the same object in memory; 2. equals is commonly used to compare whether the contents in the object are equal; 3. The equals method is composed of Object Provided by a class and can be overridden by subclasses.

Nov 11, 2019 pm 03:18 PM

javaequals==

What is the factory pattern in java

The factory pattern in Java is an instantiation object pattern that uses factory methods instead of new operations. In the factory pattern, the creation logic is not exposed to the client when creating an object, and a common interface is used to point to the newly created object.

Nov 11, 2019 pm 03:07 PM

java工厂模式

Java determines whether a character is a letter

How to determine whether a character is a letter in java: first create a function check and receive a string parameter; then take the first character of the string in the function and determine whether it is in the a-z or A-Z range; finally, based on the judgment result being true, it is concluded that the character is Just letters.

Nov 11, 2019 pm 03:02 PM

java判断字母

Java determines whether a character is empty

How to judge whether a character is empty in java: 1. Use "if(s==null || s.equals(""))" to judge, which is less efficient; 2. Use "if(s == null || s .length() == 0)" for judgment, which is more efficient and so on.

Nov 11, 2019 pm 02:45 PM

java判断字符串

what is java singleton pattern

The singleton pattern in java is a common design pattern that ensures that instances of a class are singletons. The singleton mode can save memory resources. No matter how frequently instances are created through exposed methods, the created object can be guaranteed to be the same instance object in the system memory.

Nov 11, 2019 pm 02:37 PM

java单例模式

Java gets the first few characters of a string

How to get the first few characters of a string in java: use the substring function to intercept the specified string. The first parameter is the starting index, and the second parameter is the ending index; use substring("string",3) to intercept The first three digits of the string.

Nov 11, 2019 pm 02:31 PM

java取字符串

what is reflection in java

Reflection in Java means that in the running state, any class can know what methods and properties the class has, and any object can call its methods and properties.

Nov 11, 2019 pm 02:15 PM

java反射

How to initialize an array in java

Methods for initializing arrays in java: 1. Static initialization, use arrayName = new type[]{element1,element2...} for initialization; 2. Dynamic initialization, use arrayName = new type[length] for initialization.

Nov 11, 2019 pm 02:13 PM

java数组初始化

What do keywords mean in java

Keywords in Java are words that are given specific meanings in the Java language. Keywords cannot be used as identifiers. Among them, the two special keywords goto and const in Java are called reserved words.

Nov 11, 2019 pm 01:59 PM

java关键字

How to implement java multithreading

How to implement multi-threading in Java: 1. Use the extends keyword to inherit the Thread class and override the run method to implement multi-threading; 2. Use the implements keyword to implement the Runnable interface and override the run method to implement multi-threading; 3. Through Callable implements multi-threading.

Nov 11, 2019 pm 01:55 PM

java多线程

What does exception in java mean?

An exception in Java refers to an event that occurs during program execution. Exceptions interrupt the normal instruction flow of the executing program, and exception classes must be used to effectively handle running errors in the program.

Nov 11, 2019 pm 01:41 PM

java异常什么

Generate unique random numbers java

How to generate non-repeating random numbers in java: first use the Math.random method to generate a random number; then use the contains method of ArrayList to determine whether it is repeated, and add it to the collection if it is not repeated; finally, assign the value of the collection to the array.

Nov 11, 2019 pm 01:40 PM

java不重复随机数

How to understand abstract classes in java

The abstract class in Java refers to: the class modified by the abstract keyword is an abstract class. Abstract classes cannot be instantiated, and abstract classes can have object references pointing to subclass objects.

Nov 11, 2019 pm 01:24 PM

抽象类java