Guava

Author: enjoyCoding666

src/main/java/com/guava/NewArrayListDemo.java

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+package com.guava;
+
+import com.google.common.collect.Lists;
+import com.sun.org.apache.xml.internal.security.utils.JavaUtils;
+import org.apache.commons.collections.CollectionUtils;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class NewArrayListDemo {
+
+    public static void main(String[] args) {
+        testPartition();
+
+    }
+
+
+    public static void testNewArray() {
+        ArrayList<String> arrayList = Lists.newArrayList("1", "2", "3");
+        List<String> list = Lists.newArrayList("lin","chen","wu","zhang","qiu");
+    }
+
+
+    public static void testPartition() {
+        //初始化list
+        List<String> list = Lists.newArrayList("lin","chen","wu","zhang","qiu");
+        //分页，每页2个元素
+        List<List<String>> partitionList = Lists.partition(list, 2);
+        if (CollectionUtils.size(partitionList) > 1) {
+            //下标是从0开始的，获取第2页的元素，先判断集合的size，避免数组越界。
+            List<String> partList = partitionList.get(1);
+            //结果为 [wu, qiu]
+            System.out.println(partList);
+        }
+    }
+
+
+}

src/main/java/com/guava/argument/CheckArgumentDemo.java

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+package com.guava.argument;
+
+import com.google.common.base.Preconditions;
+
+public class CheckArgumentDemo {
+
+
+    public static void main(String[] args) {
+        checkNotNull();
+    }
+
+    /**
+     * 判断空指针
+     */
+    public static void checkNotNull() {
+        String str = null;
+        Preconditions.checkNotNull(str);
+    }
+
+    /**
+     *  检查参数，不满足条件，就给出错误提示
+     *
+     */
+    public static void checkArgument() {
+        int age = 17;
+        Preconditions.checkArgument(age>=18, "年龄未满18~");
+    }
+
+
+    /**
+     *  检查参数，不满足条件，就按格式说明符替换后，给出错误提示
+     *
+     */
+    public static void checkArgumentWithFormat() {
+        String name = "lin";
+        int age = 17;
+        Preconditions.checkArgument(age>=18, "%s年龄为%s，年龄未满18",name, age);
+    }
+
+
+
+}

src/test/java/com/MapGetTest.java

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+package com;
+
+import java.util.HashMap;
+import java.util.Map;
+
+public class MapGetTest {
+    public static void main(String[] args) {
+
+//        getMap();
+
+        getOrDefaultMap();
+    }
+
+    private static void getOrDefaultMap() {
+        Map<String, Integer> map = new HashMap<>();
+        int age = map.getOrDefault("abc", 0);
+        System.out.println(age);
+
+    }
+
+    private static void getMap() {
+        Map<String, Integer> map = new HashMap<>();
+        int age = map.get("abc");
+        System.out.println(age);
+    }
+}

src/test/java/com/ObjectsTest.java

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+package com;
+
+import java.util.Objects;
+
+public class ObjectsTest {
+    public static void main(String[] args) {
+        System.out.println(toString("abc"));
+    }
+
+    public static String toString(String str) {
+        str = Objects.toString(str, "测试");
+        return str;
+    }
+}

src/test/java/com/ReorderTest.java

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+package com;
+
+import java.util.Arrays;
+import java.util.Comparator;
+import java.util.List;
+import java.util.stream.Collectors;
+
+public class ReorderTest {
+    public static void main(String[] args) {
+
+
+        sortedReverseDemo();
+
+    }
+
+    public static void sortedReverseDemo() {
+        List<Integer> list= Arrays.asList(1,3,5,7,2,4,6);
+        List<Integer> numberList = list.stream().sorted(Comparator.reverseOrder()).collect(Collectors.toList());
+        numberList.forEach(System.out::println);
+    }
+}