Preconditions provide static methods to check that a method or a
constructor is invoked with proper parameter or not. It checks the
pre-conditions. Its methods throw IllegalArgumentException on failure.
GuavaTester.java
Class Declaration
Following is the declaration for com.google.common.base.Preconditions class:@GwtCompatible public final class Preconditions extends Object
Class Methods
Sr.No | Method & Description |
---|---|
1 | static void checkArgument(boolean expression) Ensures the truth of an expression involving one or more parameters to the calling method. |
2 | static void checkArgument(boolean expression, Object errorMessage) Ensures the truth of an expression involving one or more parameters to the calling method. |
3 | static void checkArgument(boolean expression, String errorMessageTemplate, Object. errorMessageArgs) Ensures the truth of an expression involving one or more parameters to the calling method. |
4 | static int checkElementIndex(int index, int size) Ensures that index specifies a valid element in an array, list or a string of size. |
5 | static int checkElementIndex(int index, int size, String desc) Ensures that index specifies a valid element in an array, list, or a string of size. |
6 | static <T> T checkNotNull(T reference) Ensures that an object reference passed as a parameter to the calling method is not null. |
7 | static <T> T checkNotNull(T reference, Object errorMessage) Ensures that an object reference passed as a parameter to the calling method is not null. |
8 | static <T> T checkNotNull(T reference, String errorMessageTemplate, Object... errorMessageArgs) Ensures that an object reference passed as a parameter to the calling method is not null. |
9 | static int checkPositionIndex(int index, int size) Ensures that index specifies a valid position in an array, list or a string of size. |
10 | static int checkPositionIndex(int index, int size, String desc) Ensures that index specifies a valid position in an array, list or a string of size. |
11 | static void checkPositionIndexes(int start, int end, int size) Ensures that start and end specify a valid positions in an array, list or a string of size, and are in order. |
12 | static void checkState(boolean expression) Ensures the truth of an expression involving the state of the calling instance, but not involving any parameters to the calling method. |
13 | static void checkState(boolean expression, Object errorMessage) Ensures the truth of an expression involving the state of the calling instance, but not involving any parameters to the calling method. |
14 | static void checkState(boolean expression, String errorMessageTemplate, Object... errorMessageArgs) Ensures the truth of an expression involving the state of the calling instance, but not involving any parameters to the calling method. |
Methods Inherited
This class inherits methods from the following class:- java.lang.Object
Example of Preconditions
Create the following java program using any editor of your choice in say C:/> Guava.GuavaTester.java
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; } }
Verify the Result
Compile the class using javac compiler as followsC:\Guava>javac GuavaTester.javaNow run the GuavaTester to see the result.
C:\Guava>java GuavaTesterSee the result.
Illegal Argument passed: Negative value -3.0. Illegal Argument passed: First parameter is Null. Illegal Argument passed: Invalid index. (6) must be less than size (5)
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