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Server Side Programming Articles
Page 1144 of 2109
What are parametrized constructors in Java?
A constructor is similar to method and it is invoked at the time creating an object of the class, it is generally used to initialize the instance variables of a class. The constructors have same name as their class and, have no return type.Parameterized constructorsA parameterized constructor accepts parameters with which you can initialize the instance variables. Using parameterized constructor, you can initialize the class variables dynamically at the time of instantiating the class with distinct values.Syntaxpublic class Sample{ Int i; public sample(int i){ this.i = i; } }Examplepublic class Test { String ...
Read MoreHow to create a default constructor in Java?
Default constructor (No-arg constructor)A no-arg constructor doesn’t accepts any parameters, it instantiates the class variables with their respective default values (i.e. null for objects, 0.0 for float and double, false for Boolean, 0 for byte, short, int and, long).There is no need to invoke constructors explicitly these are automatically invoked at the time of instantiation.Rules to be rememberedWhile defining the constructors you should keep the following points in mind.A constructor does not have return type.The name of the constructor is same as the name of the class.A constructor cannot be abstract, final, static and Synchronized.You can use the access specifiers ...
Read MoreHow to find the sum by distinct column for factor levels in an R data frame?
If the data frame contains a factor column and some numerical columns then we might want to find the sum of numerical columns for the factor levels. For this purpose, we can use aggregate function. For example, if we have a data frame df that contains a factor column defined by Group and some numerical columns then the sum by distinct column for factor levels can be calculated by using aggregate(.~Group,data=df,sum)Example1Class
Read MoreHow to replace missing values with row means in an R data frame?
If we have similar characteristics in each column of an R data frame then we can replace the missing values with row means. To replace the missing values with row means we can use the na.aggregate function of zoo package but we would need to use the transposed version of the data frame as na.aggregate works for column means.Example1Consider the below data frame −x1
Read MoreHow to check if a variable contains number greater than 1 in an R data frame?
The variables in an R data frame are referred to as the columns of the data frame. Sometimes we have a threshold value for a particular column and we need to check whether all the values in that column are greater than or less than the threshold. For this purpose, we can make use of ifelse function as shown in the below examples.Example1y
Read MoreWhat are various ways to compare time values in Java?
The LocalTime class represents the local time i.e. the time without time zone. This class provides various methods such as isBefore(), isAfter() and, isEqual() to compare two times.Exampleimport java.time.LocalTime; public class Test { public static void main(String args[]) { LocalTime Time1 = LocalTime.of(10, 15, 45); LocalTime Time2 = LocalTime.of(07, 25, 55); Boolean bool1 = Time1.isAfter(Time2); Boolean bool2 = Time1.isBefore(Time2); if(bool1){ System.out.println(Time1+" is after "+Time2); }else if(bool2){ System.out.println(Time1+" is ...
Read MoreHow to extract unique values in multiple columns in an R data frame using a single line code?
To extract unique values in multiple columns in an R data frame, we first need to create a vector of the column values but for that we would need to read the columns in matrix form. After that we can simply unique function for the extraction. To understand how it works check out the below examples.Consider the below data frame −Examplex1
Read MoreHow to find the sum of values based on key in other column of an R data frame?
If we have a column that is key that means we want to use that column as an independent variable and find the statistical values such as sum, mean, standard deviation, range, etc. for the dependent variable. This can be done with the combination of with and tapply function as shown in the below examples.Consider the below data frame −Examplex1
Read MoreHow to find the length of the largest string in an R data frame column?
The length of the largest string can be found with the help of max function combined with nchar function. For this purpose, we first need to access the appropriate column that contains string values. Suppose, we have a data frame called df that contains a string column defined as CHAR then the length of the largest string will be found by using the command max(nchar(df$CHAR)).Consider the below data frame −Examplex
Read MoreHow to find the first quartile for a data frame column in R?
The first quartile is the value that exists at the 25th percentile, that means there are 25% of values in the data that lie below first quartile. When we find the summary of data frame the output returns this value but if we want to extract only the first quartile then quantile function can be used by specifying the percentage using 0.25.Consider the below data frame −Examplex
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