【Arrays 工具类学习】

太过爱你忘了你带给我的痛 2023-09-26 16:34 128阅读 0赞

package com.example.demomain.point.demoarray;
    
    import org.junit.Before;
    import org.junit.Test;
    
    import java.util.ArrayList;
    import java.util.Arrays;
    import java.util.Comparator;
    import java.util.List;
    import java.util.stream.Stream;
    
    /**
     *
     * Arrays 工具类学习
     *
     * @author: lfsun
     * @time: 10:38
     * @date: 2022/11/15
     */
    public class ArraysDemo {
        
        String[] initArray;
    
        @Before
        public void setUp() {
        
            initArray = new String[]{
        "冷风扇1", "冷风扇2", "冷风扇3", "冷风扇4"};
        }
    
        @Test
        public void testCopyOf() {
        
    
            String[] subArray = Arrays.copyOf(initArray, 3);
            String[] appendArray = Arrays.copyOf(initArray, 5);
            // [冷风扇1, 冷风扇2, 冷风扇3]
            printArray(subArray);
            // [冷风扇1, 冷风扇2, 冷风扇3, 冷风扇4, null]
            printArray(appendArray);
        }
    
        @Test
        public void testCopyOfRange() {
        
            // [ 0, 2 )
            String[] copyOfRangeArray = Arrays.copyOfRange(initArray, 0, 2);
            // [冷风扇1, 冷风扇2]
            printArray(copyOfRangeArray);
    
            String[] outOfIndexArray = Arrays.copyOfRange(initArray, 0, 10);
            // [冷风扇1, 冷风扇2, 冷风扇3, 冷风扇4, null, null, null, null, null, null]
            printArray(outOfIndexArray);
        }
    
        @Test
        public void testFill() {
        
            Arrays.fill(initArray, "666");
            // [666, 666, 666, 666] 进行了覆盖
            printArray(initArray);
    
            String[] emptyArray = new String[6];
            Arrays.fill(emptyArray, "999");
            // [999, 999, 999, 999, 999, 999]
            printArray(emptyArray);
        }
    
        @Test
        public void testEquals() {
        
            String[] equalsArray = {
        "冷风扇1", "冷风扇2", "冷风扇3", "冷风扇4"};
            // true
            System.out.println(Arrays.equals(initArray, equalsArray));
    
            String[] equalsArray2 = {
        "冷风扇1", "冷风扇2", "冷风扇3", "冷风扇44"};
            // false
            System.out.println(Arrays.equals(initArray, equalsArray2));
    
        }
    
        @Test
        public void testSort() {
        
            String[] sortArray = Arrays.copyOf(initArray, 4);
            System.out.println("排序前：");
            // [冷风扇1, 冷风扇2, 冷风扇3, 冷风扇4]
            printArray(sortArray);
            // 由于初始化的为正序，现改为倒序
            Arrays.sort(sortArray, Comparator.reverseOrder());
            System.out.println("排序后：");
            // [冷风扇4, 冷风扇3, 冷风扇2, 冷风扇1]
            printArray(sortArray);
    
        }
    
        @Test
        public void testBinarySearch() {
        
            // 查找到元素索引 2
            System.out.println(Arrays.binarySearch(initArray, "冷风扇3"));
            // < 0
            System.out.println(Arrays.binarySearch(initArray, "冷风扇66"));
            // 也可 加第三个参数模糊查询：/* java.util.Comparator<? super T> c*/
            System.out.println(Arrays.binarySearch(initArray, "冷风扇3", String::compareToIgnoreCase));
        }
    
        @Test
        public void testStream() {
        
            // 冷风扇1冷风扇2冷风扇3冷风扇4
            Arrays.stream(initArray).filter(e -> e.contains("冷风扇")).forEach(System.out::printf);
            System.out.println();
            System.out.println("都是闭区间 [startInclusive, endExclusive]");
            // 冷风扇1冷风扇2冷风扇3冷风扇4
            Arrays.stream(initArray, 0, initArray.length).filter(e -> e.contains("冷风扇")).forEach(System.out::printf);
            // 冷风扇1冷风扇2冷风扇3
            System.out.println();
            Arrays.stream(initArray, 0, initArray.length - 1).filter(e -> e.contains("冷风扇")).forEach(System.out::printf);
            System.out.println();
            // java.lang.ArrayIndexOutOfBoundsException: Array index out of range: -1
            // Arrays.stream(initArray, -1, initArray.length + 1).filter(e -> e.contains("冷风扇")).forEach(System.out::printf);
    
    
            System.out.println();
            // 冷风扇4冷风扇3冷风扇2冷风扇1
            Stream.of(initArray).filter(e -> e.contains("冷风扇")).sorted(Comparator.reverseOrder()).forEach(System.out::printf);
        }
    
        @Test
        public void testArray2List() {
        
            List<String> list1 = Arrays.asList(initArray);
            List<String> list2 = new ArrayList<>(Arrays.asList(initArray));
        }
    
        @Test
        public void testSetAll() {
        
            String[] intArray = new String[6];
            Arrays.setAll(intArray, index -> "1" + index);      // 最后一次 setAll 才会生效
            Arrays.setAll(intArray, index -> index + " + 0 = " + index);
            printArray(intArray);
        }
    
        @Test
        public void testSetAllPar() {
        
            String[] intArray = new String[6];
            Arrays.parallelPrefix(intArray, (left, right) -> left + " + " + right);
            // 可看到是一种累加 [null, null + null, null + null + null, null + null + null + null, null + null + null + null + null, null + null + null + null + null + null]
            printArray(intArray);
        }
    
    
        /**
         * 打印数组
         *
         * @param array
         * @param <E>
         */
        public <E> void printArray(E[] array) {
        
            System.out.println(Arrays.toString(array));
        }
    }