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Java determines whether an object is an array

The method for Java to determine whether an object is an array is: you can start from the prototype and use the "isPrototypeOf()" method to determine whether the array is in the prototype chain of obj, for example: "Array.prototype.isPrototypeOf(obj)", if so, then returns true.

Nov 21, 2019 am 11:34 AM

java judgment object array

How to determine whether a file exists in java

In Java, you can use the file.exists() method to determine whether a file exists. If the specified file or directory exists, TRUE will be returned, otherwise FALSE will be returned.

Nov 21, 2019 am 11:26 AM

java

Java determines whether a string contains numbers

Traverse a string in java and then use the java.lang.character.isDigit(); method to determine whether there are digits in it. The java.lang.character.isDigit(); method in java determines whether a character is a number.

Nov 21, 2019 am 11:04 AM

java

What is a lock in java

Java locks are used to control how multiple threads access shared resources. A lock can prevent multiple threads from accessing shared resources at the same time. The locks in Java include: synchronization lock, exclusive lock, fair lock, unfair lock, shared lock, and read-write lock.

Nov 21, 2019 am 10:47 AM

java

Java determines whether a string contains a certain character (string)

How to determine whether a string contains a certain string in Java: 1. Use the startsWith() method to determine. 2. Use the contains method to determine. 3. Use the indexOf method to judge.

Nov 21, 2019 am 10:32 AM

java

Java determines whether it is a number

How to determine whether it is a number in java: 1. Use the isDigit() function to determine. 2. Use the regular expression "[0-9]*" to judge. 3. Use digital ASCII code value to judge. 4. Judgment by catching NumberFormatException exception.

Nov 21, 2019 am 10:17 AM

java

Java determines whether it is a decimal

How to determine whether it is a decimal in Java: first convert a string of numbers into a string, and then use contains(".") to check whether there is a decimal point "." in the string to determine whether it is a decimal.

Nov 21, 2019 am 10:05 AM

java

Java uses regular expressions to determine whether the incoming data is a number

Java uses regular expressions to determine whether the incoming data is a number: you can use the regular expression "-?[0-9]+(\\.[0-9]+)?" to determine, but if the incoming data is If there are many digits, you need to use the "BigDecimal" method for conversion at the same time.

Nov 21, 2019 am 09:50 AM

java judgment number regular expression

How to get data from keyboard in java

Methods to obtain data from the keyboard in Java: You can use the Scanner class to obtain keyboard data in Java. The code for obtaining keyboard data in Java is Scanner s=new Scanner(System.in);. System.in represents the keyboard device.

Nov 21, 2019 am 09:48 AM

java

Java determines whether a collection object is empty

The method for Java to determine whether a collection object is empty is: first use the "ArrayList" implementation class to initialize the list object, then call the "isEmpty" method to determine whether the list object is empty, then execute the clear method to remove elements, and finally execute the "isEmpty" method to reset Just judge the object.

Nov 21, 2019 am 09:38 AM

java Is empty judgment

Java command is not an internal command nor an external command solution

The Java command is neither an internal command nor an external command because we did not configure the environment variables or the environment variables were configured incorrectly. We need to create and configure the JAVA_HOME and CLASSPATH variables in the environment variable settings, and then configure the PATH variable.

Nov 21, 2019 am 09:27 AM

java

How to determine whether objects are equal in java

How to determine whether objects are equal in Java: You can use the equals method. When the class does not override the equals method, compare the addresses of the two objects to see if they are equal; when the class overrides the equals method, compare whether the contents of the two objects are the same, for example: "p1.equals (p2)".

Nov 21, 2019 am 09:23 AM

java judgment object

Java determines whether it is a letter

Java can use the regular expression "[a-zA-Z]+" to determine whether it is a letter. This expression can match all letters in the string. If it is a letter, it returns true, otherwise it returns false.

Nov 21, 2019 am 09:15 AM

java

The difference between internal interface and external interface in java

The difference between internal interfaces and external interfaces in Java is that the external interface is the interface provided to the outside world (the interface provided to third parties), while the internal interface is the interface provided to the own system (the interface for internal calls within the system).

Nov 20, 2019 pm 05:29 PM

java the difference