Java interview questions summarized from many years of development experience - (2)

1. Usage of regular expressions

Define the string to be standardized -> Formulate rules -> Call the regular method

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Example:

String str = "dqwda16165"; 
String 正则表达式="[a-z]*[0-9]+"; 
system.out.println(str.matches(正则表达式)判断是否匹配)

2. How to handle exceptions in Java language, keywords: throws, throw, try, catch What do , finally mean respectively? Is the finally code executed after return or before?

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throws throws all possible exceptions throw is the specific exception type thrown try is the statement that will cause the exception to be enclosed , Exception handling catch is to execute other code if there is an exception.

finally will be executed no matter what. If there is a return in try or catch, after the return is executed, it will wait for finally to complete before returning.

3. What is the difference between abstract class and interface? Can an interface inherit an interface? Can an interface inherit from an abstract class? Why?

The difference between abstract classes and interfaces: Abstract methods in abstract classes must be implemented by subclasses. Abstract classes can inherit multiple abstract classes. Ordinary classes can only inherit one abstract class and cannot have a main method. They can have ordinary methods. Abstract methods are modified by public abstract by default.

Only abstract methods can be written in interface classes. Properties are modified by public static final by default. Multiple interfaces can be implemented by the same class.

4. Can the constructor be overridden?

Constructor (constructor) cannot be inherited and cannot be overridden, but it can be overloaded.

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5. Can the String class be inherited?

public final class String extends Object, which contains the final keyword, so it cannot be inherited.

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