编码练习——Java-数组-API-练习

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java.util.Arrays

Arrays.asList()

• 数组转换成列表

String[] strArray = {"zhang", "xue", "zhi"};List<String> list = Arrays.asList(strArray);// 打印元素for (int i=0; i<list.size(); i++) {    System.out.print(list.get(i) + " ");}

Arrays.binarySearch()

• 二分查找
• 查找前，一定要排序。
• 如果查找元素不存在，返回(-(insertion point) - 1)。
• 自然数表示查到，负数表示没有查找。

int[] a = {3,5,9,7,2};Arrays.sort(a); // 排序// 打印数组for (int item : a)     System.out.print(item + " ");System.out.println();// 二分查找int ind1 = Arrays.binarySearch(a, 2);int ind2 = Arrays.binarySearch(a, 4);int ind3 = Arrays.binarySearch(a, 1, 3, 5);System.out.println("2的查找位置：" + ind1);System.out.println("4的查找位置：" + ind2);System.out.println("5的查找位置：" + ind3);// 字符串String[] strArray = {"aa", "bc", "ab", "cd"};Arrays.sort(strArray);int ind4 = Arrays.binarySearch(strArray, "bc");System.out.println("'bc'的查找位置是：" + ind4);

Arrays.copyOf()

• 复制长度大于原数组长度时，后面补零。

int[] a = {3,5,9,7,2};int[] newa = Arrays.copyOf(a, 2);int[] newa2 = Arrays.copyOf(a, 7);  //复制长度大于原数组的长度for (int item : newa)     System.out.print(item + " ");System.out.println();for (int item : newa2)     System.out.print(item + " ");System.out.println();

Arrays.copyOfRange()

• 复制长度大于原数组长度时，后面补零。
• Java中区间一般都是左闭右开[a,b)，即包括左边，不包括右边。

int[] a = {3,5,9,7,2};int[] newa = Arrays.copyOfRange(a, 1, 3);int[] newa2 = Arrays.copyOfRange(a, 1, 8);  //复制长度大于原数组的长度for (int item : newa)     System.out.print(item + " ");System.out.println();for (int item : newa2)     System.out.print(item + " ");System.out.println();

Arrays.deepEquals()

• 比较数组元素是否深层相等。
• 一维数组无区别，高维数组有区别。

String[][] ticTacToe1 = { { " O ", " O ", " X " }, { " O ", " X ", " X " },{ " X ", " O ", " O " } };String[][] ticTacToe2 = { { " O ", " O ", " X " }, { " O ", " X ", " X " },{ " X ", " O ", " O " } };System.out.println(Arrays.equals(ticTacToe1, ticTacToe2));// falseSystem.out.println(Arrays.deepEquals(ticTacToe1, ticTacToe2));// trueString[] ticTacToe3 = { " O ", " O ", " X " };String[] ticTacToe4 = { " O ", " O ", " X " };  System.out.println(Arrays.equals(ticTacToe3, ticTacToe4));  // trueSystem.out.println(Arrays.deepEquals(ticTacToe3, ticTacToe4));  // true

Arrays.deepHashCode()

• 深层相等的两个数组的深层哈希编码也相等。

String[][] ticTacToe1 = { { " O ", " O ", " X " }, { " O ", " X ", " X " },{ " X ", " O ", " O " } };String[][] ticTacToe2 = { { " O ", " O ", " X " }, { " O ", " X ", " X " },{ " X ", " O ", " O " } };System.out.println(Arrays.equals(ticTacToe1, ticTacToe2));// falseSystem.out.println(Arrays.deepEquals(ticTacToe1, ticTacToe2));// true// ticTacToe1和ticTacToe1深层相等，深层哈希编码也相等。System.out.println(Arrays.deepHashCode(ticTacToe1));System.out.println(Arrays.deepHashCode(ticTacToe2));

Arrays.deepToString()

// 二维数组有区别String[][] ticTacToe1 = { { " O ", " O ", " X " }, { " O ", " X ", " X " },{ " X ", " O ", " O " } };System.out.println(Arrays.deepToString(ticTacToe1));    // 深层变换成字符串System.out.println(Arrays.toString(ticTacToe1));        // 一般// 一维数组无区别String[] ticTacToe3 = { " O ", " O ", " X " };System.out.println(Arrays.deepToString(ticTacToe3));    // 深层变换成字符串System.out.println(Arrays.toString(ticTacToe3));        // 一般

Arrays.equals()

• 参考Arrays.deepArrays()

Arrays.fill()

• 填充数组元素

int[] a = {1,2,3,4,5,6};Arrays.fill(a, 8);//全部填充for (int item : a)     System.out.print(item + " ");System.out.println();Arrays.fill(a, 1, 3, 0);//指定范围，替换for (int item : a)     System.out.print(item + " ");

Arrays.hashCode()

• 如果两个数组相等，哈希编码也相等。

int[] a = {1,2,3,4,5,6};int[] b = {1,2,3,4,5,6};String[] c = {"a", "b", "c"};String[] d = {"a", "b", "c"};System.out.println("a==b:" + Arrays.equals(a, b));System.out.println("a和b的哈希码分别为：" + Arrays.hashCode(a) + "\t" + Arrays.hashCode(b));// 字符串System.out.println("c==d:" + Arrays.equals(c, d));System.out.println("c和d的哈希码分别为：" + Arrays.hashCode(c) + "\t" + Arrays.hashCode(d));System.out.println("c==d:" + c.equals(d));System.out.println("c和d的哈希码分别为：" + c.hashCode() + "\t" + d.hashCode());

Arrays.sort()

int[] a = {6,5,4,3,2,1};// 指定范围排序Arrays.sort(a, 1, 4);for (int item : a)     System.out.print(item + " ");System.out.println();// 全部元素排序Arrays.sort(a);for (int item : a)     System.out.print(item + " ");System.out.println();

Arrays.toString()

• 参考 Arrays.deepToString()

遍历数组

遍历一维数组

int[] a = {6,5,4,3,2,1};// 遍历数组 forfor (int i=0; i<a.length; i++)    if (i == a.length-1)        System.out.print(a[i]);    else        System.out.print(a[i] + ", ");System.out.println();// 遍历数组  - foreachfor (int item : a)    if (item == a[a.length-1])        System.out.print(item);    else         System.out.print(item + ", ");

遍历二维数组

int[][] a = {{1,2,3}, {4,5,6}, {7,8,9}};// 遍历二维数组 forfor (int i=0; i<a.length; i++) {    for (int j=0; j<a[i].length; j++)        if (j == a[i].length-1)            System.out.print(a[i][j]);        else            System.out.print(a[i][j] + ", ");    System.out.println();}

数组对象的方法

• 数组从java.lang.Object继承的方法：clone, equals, finalize, getClass, hashCode, notify, toString, wait

arr.clone()

• 通过克隆生成另一个数组

int[] a = {1,2,3,4,5,6};int[] b = a.clone();Arrays.fill(a, 1, 4, 0); // 改变a，看是否对b有影响//打印bfor (int item : b)     System.out.print(item + " ");

arr.equals()

• arr.equals()和Arrays.equals()不同

int[] a = {1,2,3,4,5,6};int[] b = a.clone();int[] c = a;// 判等System.out.println(Arrays.equals(a, b)); // 比较内容System.out.println(a.equals(b));    //比较地址System.out.println(a.equals(c));

arr.getClass()

int[] a = {1,2,3,4,5,6};System.out.println(a.getClass());

arr.hashCode()

int[] a = {1,2,3,4,5,6};// 两种方法的结果不同。System.out.println(a.hashCode()); System.out.println(Arrays.hashCode(a)); // Arrays.hashCode()

arr.toString()

int[] a = {1,2,3,4,5,6};System.out.println(a.toString());   // 地址System.out.println(Arrays.toString(a)); //字符串

数组对象的属性

arr.length

int[] a = {1,2,3,4,5,6};int len = a.length;System.out.println(len);