Defining a Simple Generic Class in Java

A generic class is a class with one or more type variables. In this chapter, we will use a simple Pair class as an example. This class allows us to focus on generics without being distracted by data storage details. Here is the code for the generic Pair class:

public class Pair<T>


private T first;

private T second;


public Pair() { first = null; second = null; }

public Pair(T first, T second) { this.first = first; this.second = second; }


public T getFirst() { return first; }

public T getSecond() { return second; }


public void setFirst(T newValue) { first = newValue; }

public void setSecond(T newValue) { second = newValue; }


The Pair class introduces a type variable T, enclosed in angle brackets < >, after the class name. A generic class can have more than one type variable. For example, we could have defined the Pair class with separate types for the first and second field:

public class Pair<T, U> { . . . }

The type variables are used throughout the class definition to specify method return types and the types of fields and local variables. For example:

private T first; // uses the type variable

You instantiate the generic type by substituting types for the type variables, such as


You can think of the result as an ordinary class with constructors



and methods

String getFirst()

String getSecond()

void setFirst(String)

void setSecond(String)

In other words, the generic class acts as a factory for ordinary classes.

The program in Listing 8.1 puts the Pair class to work. The static minmax method traverses an array and simultaneously computes the minimum and maximum values. It uses a Pair object to return both results. Recall that the compareTo method compares two strings, returning 0 if the strings are identical, a negative integer if the first string comes before the second in dictionary order, and a positive integer otherwise.

Source: Horstmann Cay S. (2019), Core Java. Volume I – Fundamentals, Pearson; 11th edition.

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