本文主要是介绍Java学习笔记（day42），对大家解决编程问题具有一定的参考价值，需要的程序猿们随着小编来一起学习吧！

一、学习内容

主题：哈希表

定义：根据关键码值(Key value)而直接进行访问的数据结构。也就是说，它通过把关键码值映射到表中一个位置来访问记录，以加快查找的速度。这个映射函数叫做散列函数，存放记录的数组叫做散列表。
给定表M，存在函数f(key)，对任意给定的关键字值key，代入函数后若能得到包含该关键字的记录在表中的地址，则称表M为哈希(Hash）表，函数f(key)为哈希(Hash) 函数。

二、代码编写

/**
	 *********************
	 * The second constructor. For Hash code only. It is assumed that
	 * paraKeyArray.length <= paraLength.
	 * 
	 * @param paraKeyArray     The array of the keys.
	 * @param paraContentArray The array of contents.
	 * @param paraLength       The space for the Hash table.
	 *********************
	 */
	public DataArray(int[] paraKeyArray, String[] paraContentArray, int paraLength) {
		// Step 1. Initialize.
		length = paraLength;
		data = new DataNode[length];

		for (int i = 0; i < length; i++) {
			data[i] = null;
		} // Of for i

		// Step 2. Fill the data.
		int tempPosition;

		for (int i = 0; i < paraKeyArray.length; i++) {
			// Hash.
			tempPosition = paraKeyArray[i] % paraLength;

			// Find an empty position
			while (data[tempPosition] != null) {
				tempPosition = (tempPosition + 1) % paraLength;
				System.out.println("Collision, move forward for key " + paraKeyArray[i]);
			} // Of while

			data[tempPosition] = new DataNode(paraKeyArray[i], paraContentArray[i]);
		} // Of for i
	}// Of the second constructor

	/**
	 *********************
	 * Hash search.
	 * 
	 * @param paraKey The given key.
	 * @return The content of the key.
	 *********************
	 */
	public String hashSearch(int paraKey) {
		int tempPosition = paraKey % length;
		while (data[tempPosition] != null) {
			if (data[tempPosition].key == paraKey) {
				return data[tempPosition].content;
			} // Of if
			System.out.println("Not this one for " + paraKey);
			tempPosition = (tempPosition + 1) % length;
		} // Of while

		return "null";
	}// Of hashSearch

	/**
	 *********************
	 * Test the method.
	 *********************
	 */
	public static void hashSearchTest() {
		int[] tempUnsortedKeys = { 16, 33, 38, 69, 57, 95, 86 };
		String[] tempContents = { "if", "then", "else", "switch", "case", "for", "while" };
		DataArray tempDataArray = new DataArray(tempUnsortedKeys, tempContents, 19);

		System.out.println(tempDataArray);

		System.out.println("Search result of 95 is: " + tempDataArray.hashSearch(95));
		System.out.println("Search result of 38 is: " + tempDataArray.hashSearch(38));
		System.out.println("Search result of 57 is: " + tempDataArray.hashSearch(57));
		System.out.println("Search result of 4 is: " + tempDataArray.hashSearch(4));
	}// Of hashSearchTest

	/**
	 *********************
	 * The entrance of the program.
	 * 
	 * @param args Not used now.
	 *********************
	 */
	public static void main(String args[]) {
		System.out.println("\r\n-------sequentialSearchTest-------");
		sequentialSearchTest();

		System.out.println("\r\n-------binarySearchTest-------");
		binarySearchTest();

		System.out.println("\r\n-------hashSearchTest-------");
		hashSearchTest();
	}// Of main

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