只讀設定

• Test01_ReadOnly.java

package guava.collection;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

import com.google.common.collect.ImmutableList;
/**
 * 只讀設定
 * 1.原始(重新包裝)：將需要設定為只讀的容器用Collections.unmodifiable_xxx()包裝成一個新的容器;
 * 2.現在(直接建立)：直接用Immutable_xxx.of(元素...)建立一個新的容器
 */
 

public class Test01_ReadOnly {
    public static void main(String[] args) {

        List<String> list =new ArrayList<String>();
        list.add("a");
        list.add("b");
        list.add("c");
        //對原有的list進行包裝，相等於原有List的一個檢視，快照，不夠安全
        List<String> readList =Collections.unmodifiableList(list);
        readList.add("d"
 
);//java.lang.UnsupportedOperationException
        list.add("d"); //改變原有List;檢視也一起改變

        //對比 檢視 初始化List guava對只讀設定 安全可靠，並且相對簡單
        List<String> immutableList =ImmutableList.of("a", "b", "c"); 
        immutableList.add("d");//java.lang.UnsupportedOperationException
    }
}

函數語言程式設計(過濾|轉換|組合式程式設計)

• Test02_Function.java

package guava.collection;

import java.text.SimpleDateFormat;
import java.util.Collection;
import java.util.List;
import java.util.Set;

import com.google.common.base.Function;
import com.google.common.base.Functions;
import com.google.common.base.Predicate;
import com.google.common.collect.Collections2;
import com.google.common.collect.Lists;
import com.google.common.collect.Sets;
/**
 * 函數語言程式設計 :解耦
 * 1.Predicate
     Predicate<T> pre=new Predicate<T>() {
        @Override
        public boolean apply(T input) {
            return false;
        }
    };

 * 2.Function
 *   Function<F, T> fun=new Function<F, T>() {
        @Override
        public T apply(F input) {
            return null;
        }
     };
 * 
 * 工具:
 * Collections2.filter(容器,Predicate) 過濾器
 * Collections2.transfer(容器,Function) 轉換
 * Function newf=Functions.compose(f1,f2...)組合式函式程式設計
 */
public class Test02_Function {
    public static void main(String[] args) {
        test1();//過濾器
        test2();//轉換
        test3();//組合式函式程式設計

    }

    /**過濾器*/
    public static void test1(){
        //建立List;靜態初始化
        List<String> list =Lists.newArrayList("moom","son","dad","bjsxt","refer");
        //找出迴文 palindrome; backwords; mirror words
        //匿名內部類物件: 匿名內部類，同時建立類物件

        Collection<String> palindromeList =Collections2.filter(list, new Predicate<String>(){
            @Override
            public boolean apply(String input) {
                //業務邏輯
                return new StringBuilder(input).reverse().toString().equals(input);
            }
        });

        for(String temp:palindromeList){
            System.out.println(temp);
        }
    }

    /**轉換*/
    public static void test2(){
        //型別轉換
        Set<Long> timeSet =Sets.newHashSet();
        timeSet.add(10000000L);
        timeSet.add(99999999999999999L);
        timeSet.add(2000000000L);

        Collection<String> timeStrCol =Collections2.transform(timeSet, new Function<Long,String>(){
            @Override
            public String apply(Long input) {
                return new SimpleDateFormat("yyyy-MM-dd").format(input);
            }
        });

        for(String temp:timeStrCol){
            System.out.println(temp);
        }
    }
    /**
     * 組合式函式程式設計
     */
    public static void test3(){
        //確保容器中的字串長度不超過5,超過進行擷取,後全部大寫
        List<String> list =Lists.newArrayList("bjsxt","good","happiness");
        //確保容器中的字串長度不超過5,超過進行擷取
        Function<String,String> f1 =new Function<String,String>(){
            @Override
            public String apply(String input) {
                return input.length()>5?input.substring(0,5):input;
            }
        };
        //轉成大寫
        Function<String,String> f2 =new Function<String,String>(){
            @Override
            public String apply(String input) {
                return input.toUpperCase();
            }
        };

        //String =f2(f1(String))
        Function<String,String> f =Functions.compose(f1, f2);
        Collection<String> resultCol =Collections2.transform(list, f);
        for(String temp:resultCol){
            System.out.println(temp);
        }
    }
}

加入約束條件

• Test03_Constraint.java

package guava.collection;

import java.util.Set;

import com.google.common.collect.Constraint;
import com.google.common.collect.Constraints;
import com.google.common.base.Preconditions;
import com.google.common.collect.Sets;

/**
 * 加入約束條件:Constraint,Preconditions,Constraints
 * Constraint<E> constraint=new Constraint<E>() {
        @Override
        public E checkElement(E element) {
        Preconditions.checkNotNull(element);//非空驗證
        Preconditions.checkArgument(element.length()>=5 && element.length()<=20);//長度驗證
            return element;
        }
    };
 * Constraints.constrained_xxx(需要約束的容器, constraint);//返回一個容器
 */
public class Test03_Constraint {
    public static void main(String[] args) {
        Set<String> sets =Sets.newHashSet();
        //建立約束

        Constraint<String> constraint =new Constraint<String>(){
            @Override
            public String checkElement(String element) {
                //非空驗證
                Preconditions.checkNotNull(element);
                //長度驗證 5-20為字串
                Preconditions.checkArgument(element.length()>=5 && element.length()<=20);
                return element;
            }
        };
        Set<String> cs =Constraints.constrainedSet(sets, constraint);
//      cs.add(null); //java.lang.NullPointerException
//      cs.add("good"); //java.lang.IllegalArgumentException
        cs.add("bjsxt");
        for(String str:cs){
            System.out.println(str);
        }
    }
}

集合的操作

• Test04_GatherOperation.java

package guava.collection;

import java.util.Set;

import com.google.common.collect.Sets;
import com.google.common.collect.Sets.SetView;
/**
 * 集合的操作:
 * 1. 交集
 *    Sets.intersection()
 * 2. 差集
 *    Sets.difference()
 * 3. 並集
 *    Sets.union();
 */
public class Test04_GatherOperation {
    public static void main(String[] args) {
        Set<Integer> sets =Sets.newHashSet(1,2,3,4,5,6);
        Set<Integer> sets2 =Sets.newHashSet(3,4,5,6,7,8,9);

        //交集
        System.out.println("交集為:");
        SetView<Integer> intersection =Sets.intersection(sets, sets2);
        for(Integer temp:intersection){
            System.out.println(temp);
        }
        //差集
        System.out.println("差集為:");
        SetView<Integer> diff =Sets.difference(sets, sets2);
        for(Integer temp:diff){
            System.out.println(temp);
        }
        //並集
        System.out.println("並集為:");
        SetView<Integer> union =Sets.union(sets, sets2);
        for(Integer temp:union){
            System.out.println(temp);
        }
    }
}