java Interview.java的Java技巧

Posted 2021-05-08

import java.util.ArrayList;

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

	// String
	String s = "abc";
	s.charAt(0);
	s.length();
	s.substring(0, 1);
	s.substring(1);
	s.equals("b");
	s = s.trim();
	s.indexOf("a");
	s.indexOf("a", 1);
	s.lastIndexOf("a");
	s.indexOf("a", 1);
	s.toCharArray();
	Integer.valueOf(s); // returns an Integer object
	Integer.parseInt(s); // returns an int primitive
	String.valueOf(s); // integer to string

	// StringBuilder
	sb.reverse();
	sb.toString();

	// Array
	int[] a = new int[10];
	char[] b = {'a','b'};
	int[][] c = new int[10][10];
	int m = a.length;
	StringBuilder sb = new StringBuilder();
	sb.append("a");
	sb.insert(0, "a");
	sb.deleteCharAt(sb.length() ‐ 1);
	int n = c[0].length;
	int max = Integer.MAX_VALUE;
	int min = Integer.MIN_VALUE;
	Arrays.sort(a);
	for(int i=0; i<c.length; i++){
		 System.out.println(c[i]);
	}

	// List
	List<Integer> list = new ArrayList<Integer>();
	ArrayList<Integer> list1 = new ArrayList<Integer>();
	List<List<Integer>> list2 = new ArrayList<List<Integer>>();
	list.add(0);
	list.add(0, 1);
	list.get(0);
	list.size();
	list.remove(list.size() ‐ 1);
	Collections.sort(list);
	Collections.sort(list, Collections.reverseOrder());
	Collections.sort(list, new Comparator<Integer>() {
		@Override
		public int compare(Integer o1, Integer o2) {
		return o1 ‐ o2;// 0‐>1
		// return o2‐o1; 1‐>0
		}
	});

	// Stack
	Stack<Integer> stack = new Stack<Integer>();
	stack.push(0);
	stack.pop();
	stack.peek();
	stack.isEmpty();
	stack.size();
	
	// Queue add ‐‐‐‐‐‐> remove, peek
	Queue<Integer> q = new LinkedList<Integer>();
	q.add(0);
	q.remove();
	q.peek();
	q.isEmpty();
	q.size();

	// HashMap
	HashMap<Character, Integer> map = new HashMap<Character, Integer>();
	map.put('c', 1);
	map.get('c');
	if (map.containsKey('c')) {}
	if (map.containsValue(1)) {}
	for (Character d : map.keySet()) {}
	for (Integer i : map.values()) {}
	map.isEmpty();
	map.size();

	// HashSet
	HashSet<Integer> set = new HashSet<Integer>();
	set.add(0);
	set.remove(0);
	if (set.contains(0)) {}
	set.isEmpty();
	set.size();
	
	// mini heap
	PriorityQueue<Integer> pq = new PriorityQueue<Integer>();
	pq.add(0);
	pq.remove();
	pq.peek();
	pq.isEmpty();
	pq.size();
  while (!pq.isEmpty()) {}
 }
}