Guava Preconditions类

1 什么是Guava Preconditions类

Preconditions类提供静态方法来检查方法或构造函数是否使用正确的参数调用。它检查先决条件。它的方法在失败时抛出 IllegalArgumentException异常。

2 Guava Preconditions类的语法

@GwtCompatible
public final class Preconditions
   extends Object

3 Guava Preconditions类的方法

5 Guava Preconditions类的例子

让我们看一个简单的Guava Preconditions类示例。

package cn.xnip;

import com.google.common.base.Preconditions;

public class GuavaTester {

   public static void main(String args[]) {
      GuavaTester guavaTester = new GuavaTester();

      try {
         System.out.println(guavaTester.sqrt(-3.0));
      } catch(IllegalArgumentException e) {
         System.out.println(e.getMessage());
      }

      try {
         System.out.println(guavaTester.sum(null,3));
      } catch(NullPointerException e) {
         System.out.println(e.getMessage());
      }

      try {
         System.out.println(guavaTester.getValue(6));
      } catch(IndexOutOfBoundsException e) {
         System.out.println(e.getMessage());
      }
   }

   public double sqrt(double input) throws IllegalArgumentException {
      Preconditions.checkArgument(input > 0.0,
         "Illegal Argument passed: Negative value %s.", input);
      return Math.sqrt(input);
   }

   public int sum(Integer a, Integer b) {
      a = Preconditions.checkNotNull(a, "Illegal Argument passed: First parameter is Null.");
      b = Preconditions.checkNotNull(b, "Illegal Argument passed: Second parameter is Null.");

      return a+b;
   }

   public int getValue(int input) {
      int[] data = {1,2,3,4,5};
      Preconditions.checkElementIndex(input,data.length, "Illegal Argument passed: Invalid index.");
      return 0;
   }
}

输出结果为：