Guava入门第三章(Preconditions)

Preconditions详细介绍

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package com.lvshihao.guava;

import com.google.common.base.Preconditions;
import com.google.common.collect.ImmutableList;
import org.junit.Test;
import java.util.List;

import static org.hamcrest.core.Is.is;
import static org.hamcrest.core.IsEqual.equalTo;
import static org.junit.Assert.assertThat;

/**
 *@author: LVSHIHAO
 *@description: GUAVA Preconditions detailed introduction
 */
public class PreconditionsTest {

    @Test(expected = NullPointerException.class)
    public void testCheckNotNull(){
        checkNotNull(null);
    }

    @Test
    public void testCheckNotNullWithMessage(){
       try{
           checkNotNullWithMessage(null);
       }catch (Exception e){
          assertThat(e,is(NullPointerException.class));
          assertThat(e.getMessage(),equalTo("The list should not be null"));
       }
    }

    @Test
    public void testCheckNotNullWithFormatMessage(){
        try{
            checkNotNullWithFormatMessage(null);
        }catch (Exception e){
            assertThat(e,is(NullPointerException.class));
            assertThat(e.getMessage(),equalTo("The list should not be null and the size must be 2"));
        }
    }

    @Test
    public void testCheckArguments(){
        /**
         * Preconditions.checkArgument(); 检查传入的参数是否合法,false 抛出IllegalArgumentException异常
         * Check whether the passed parameter is legitimate , false throws IllegalArgumentException
         */
        try{
            final String type ="A";
            Preconditions.checkArgument(type.equals("B"));
        }catch (Exception e){
            assertThat(e,is(IllegalArgumentException.class));
        }
    }

    @Test
    public void testCheckState(){
        /**
         * Preconditions.checkArgument(); 检查传入的状态是否合法,false IllegalStateException
         * Check whether the incoming state is legal, false throws IllegalStateException
         */
        try{
            final String state ="A";
            Preconditions.checkState(state.equals("B"),"The state is illegal.");
        }catch (Exception e){
            assertThat(e,is(IllegalStateException.class));
            assertThat(e.getMessage(),equalTo("The state is illegal."));
        }
    }

    @Test
    public void testCheckIndex(){
        /**
         * Preconditions.checkElementIndex(); 检查传入的Index是否越界,如果比传入集合的下标大就会抛出 IndexOutOfBoundsException
         * CCheck whether the incoming Index is out of bounds, if it is larger than the subscript of the incoming collection, it will be thrown IndexOutOfBoundsException
         */
        try{
            ImmutableList<Object> list = ImmutableList.of("2");
            Preconditions.checkElementIndex(0,list.size());
        }catch (Exception e){
            assertThat(e,is(IndexOutOfBoundsException.class));
        }
    }


    private void checkNotNull(final List<String> list){
        /**
         * Preconditions.checkNotNull() 检查是否为null,如果为null 抛出NullPointerException异常，否则返回数据
         * checkout is not null if is null throw NullPointerException Exception else return data
         */
        Preconditions.checkNotNull(list);
    }

    private void checkNotNullWithMessage(final List<String> list){
        /**
         * 传入Message异常信息    incoming Exception Message
         */
        Preconditions.checkNotNull(list,"The list should not be null");
    }


    private void checkNotNullWithFormatMessage(final List<String> list){
        /**
         * 格式化异常信息    format Exception Message
         */
        Preconditions.checkNotNull(list,"The list should not be null and the size must be %s",2);
    }
}