Java – Random Long, Float, Integer and Double – Java – 随机的Long, Float, Integer and Double

最后修改: 2014年 7月 20日

This quick tutorial will illustrate how to generate a long first using plain Java and using the Apache Commons Math library.

这个快速教程将说明如何使用普通的Java和使用Apache Commons数学库来生成一个长的第一。

This article is part of the “Java – Back to Basic” series here on Baeldung.

本文是Baeldung网站上“Java – Back to Basic “系列的一部分。

1. Generate an Unbounded Long


Let’s start with generating a Long:


public void givenUsingPlainJava_whenGeneratingRandomLongUnbounded_thenCorrect() {
    long generatedLong = new Random().nextLong();

2. Generate a Long Within a Range


2.1. Random Long With Plain Java


Next – let’s look at creating a random bounded Long – that is, a Long value within a given range or interval:


public void givenUsingPlainJava_whenGeneratingRandomLongBounded_thenCorrect() {
    long leftLimit = 1L;
    long rightLimit = 10L;
    long generatedLong = leftLimit + (long) (Math.random() * (rightLimit - leftLimit));

2.2. Random Long With Apache Commons Math

2.2.使用Apache Commons数学的随机长

Let’s take a look at generating the random Long with a cleaner API and Commons Math:

让我们来看看用更干净的API和Commons Math生成随机Long的情况。

public void givenUsingApacheCommons_whenGeneratingRandomLongBounded_thenCorrect() {
    long leftLimit = 10L;
    long rightLimit = 100L;
    long generatedLong = new RandomDataGenerator().nextLong(leftLimit, rightLimit);

3. Generate an Unbounded Integer


Let’s move right on to generating a random Integer with no bounds:


public void givenUsingPlainJava_whenGeneratingRandomIntegerUnbounded_thenCorrect() {
    int generatedInteger = new Random().nextInt();

As you can see, it’s pretty close to generating a long.


4. Generate an Integer Within a Range


4.1. Random Integer With Plain Java


Next – a random integer within a given range:

下一个 – 在给定范围内的一个随机整数。

public void givenUsingPlainJava_whenGeneratingRandomIntegerBounded_thenCorrect() {
    int leftLimit = 1;
    int rightLimit = 10;
    int generatedInteger = leftLimit + (int) (new Random().nextFloat() * (rightLimit - leftLimit));

4.2. Random Integer With Commons Math

4.2.使用Commons Math的随机整数

And the same with Common Math:


public void givenUsingApache_whenGeneratingRandomIntegerBounded_thenCorrect() {
    int leftLimit = 1;
    int rightLimit = 10;
    int generatedInteger = new RandomDataGenerator().nextInt(leftLimit, rightLimit);

5. Generate an Unbounded Float


Now, let’s go over generating random floats – first unbounded:


public void givenUsingPlainJava_whenGeneratingRandomFloatUnbouned_thenCorrect() {
    float generatedFloat = new Random().nextFloat();

6. Generate a Float Within a Range


6.1. Random Float With Plain Java


And a bounded random float:


public void givenUsingPlainJava_whenGeneratingRandomFloatBouned_thenCorrect() {
    float leftLimit = 1F;
    float rightLimit = 10F;
    float generatedFloat = leftLimit + new Random().nextFloat() * (rightLimit - leftLimit);

6.2. Random Float With Commons Math


Now – a bounded random float with Commons Math:


public void givenUsingApache_whenGeneratingRandomFloatBounded_thenCorrect() {
    float leftLimit = 1F;
    float rightLimit = 10F;
    float randomFloat = new RandomDataGenerator().getRandomGenerator().nextFloat();
    float generatedFloat = leftLimit + randomFloat * (rightLimit - leftLimit);

7. Generate an Unbounded Double


7.1. Random Unbounded Double With Plain Java


Finally – we’re going to generate random double values – first, with the Java Math API:

最后–我们要生成随机的双倍值–首先,用Java Math API。

public void givenUsingPlainJava_whenGeneratingRandomDoubleUnbounded_thenCorrect() {
    double generatedDouble = Math.random();

7.2. Random Unbounded Double With Commons Math


As well as a random double value with the Apache Commons Math library:

以及用Apache Commons数学库的随机双倍值。

public void givenUsingApache_whenGeneratingRandomDoubleUnbounded_thenCorrect() {
    double generatedDouble = new RandomDataGenerator().getRandomGenerator().nextDouble();

8. Generate a Double Within a Range


8.1. Random Bounded Double With Plain Java


In this example, let’s take a look at a random double generated within an interval – with Java:


public void givenUsingPlainJava_whenGeneratingRandomDoubleBounded_thenCorrect() {
    double leftLimit = 1D;
    double rightLimit = 10D;
    double generatedDouble = leftLimit + new Random().nextDouble() * (rightLimit - leftLimit);

8.2. Random Bounded Double With Commons Math


And lastly – a random double within an interval, using the Apache Commons Math library:

最后–使用Apache Commons数学库,在一个区间内随机生成一个双数。

public void givenUsingApache_whenGeneratingRandomDoubleBounded_thenCorrect() {
    double leftLimit = 1D;
    double rightLimit = 100D;
    double generatedDouble = new RandomDataGenerator().nextUniform(leftLimit, rightLimit);

And there you have it – quick and to the point examples of how to generate both unbounded and bounded values for the most common numerical primitives in Java.


9. Conclusion


This tutorial illustrated how we could generate random numbers either bound or unbound, using different techniques and libraries.


As always, the implementation of all of these examples and snippets can be found in the GitHub project. This is a Maven-based project so it should be easy to import and run.