Algorithm

• leetcode 300: Longest Increasing Subsequence

代碼地址：https://github.com/Lazy-Lion/Algorithm/blob/master/java/src/dynamicprogramming/LongestIncreasingSubsequence.java

• leetcode 44: Wildcard Matching

代碼地址： https://github.com/Lazy-Lion/Algorithm/blob/master/java/src/dynamicprogramming/WildcardMatching.java

Review

Strings, Literally
文章介紹了java 中String字面量以及String對象的一些知識點殖侵。

針對String字面量進行如下的代碼測試 (JDK8):

public class StringTest {
    static String temp3 = "CD";
    final static String temp4 = "CD";
     
    public static void main(String[] args) {
         
        String s1 = "ABCD";
        String s2= "A" + "B" + "C" + "D";
         
        String temp = "CD";
        String s3 = "AB" + temp;
         
        final String temp2 = "CD";
        String s4 = "AB" + temp2;

        String s5 = "AB" + temp3;
         
        String s6 = "AB" + temp4;
         
        String s7 = "AB" + get();
         
        String s8 = "AB" + getF();
         
        //tip: 編寫代碼System.out.println("s1 == s2 ? " + s1 == s2); 漏寫括號，
        //導致輸出的是"(s1 == s2 ? " + s1) == s2" 的結(jié)果
        System.out.println("s1 == s2 ? " + (s1 == s2));  
        System.out.println("s1 == s3 ? " + (s1 == s3));
        System.out.println("s1 == s4 ? " + (s1 == s4));
        System.out.println("s1 == s5 ? " + (s1 == s5));
        System.out.println("s1 == s6 ? " + (s1 == s6));
        System.out.println("s1 == s7 ? " + (s1 == s7));
        System.out.println("s1 == s8 ? " + (s1 == s8));
    }
     
    public static String get(){
        return "CD";
    }
     
    public final static String getF(){
        return "CD";
    }
}

對上述代碼進行反編譯：

public class StringTest {
    static String temp3 = "CD";
    static final String temp4 = "CD";
 
    public static void main(String[] args) {
        String s1 = "ABCD";
        String s2 = "ABCD";
        String temp = "CD";
        String s3 = "AB" + temp;
        String temp2 = "CD";
        String s4 = "ABCD";
        String s5 = "AB" + temp3;
        String s6 = "ABCD";
        String s7 = "AB" + get();
        String s8 = "AB" + getF();
        System.out.println("s1 == s2 ? " + (s1 == s2));
        System.out.println("s1 == s3 ? " + (s1 == s3));
        System.out.println("s1 == s4 ? " + (s1 == s4));
        System.out.println("s1 == s5 ? " + (s1 == s5));
        System.out.println("s1 == s6 ? " + (s1 == s6));
        System.out.println("s1 == s7 ? " + (s1 == s7));
        System.out.println("s1 == s8 ? " + (s1 == s8));
    }
 
    public static String get() {
        return "CD";
    }
 
    public static final String getF() {
        return "CD";
    }
}

可以看到烙如，對于"+"連接，編譯期間存在部分優(yōu)化：

• "+" 直接連接多個字面量液茎，編譯期間優(yōu)化成一個字面量
• "+" 連接字面量和final變量票彪，編譯期間優(yōu)化成一個字面量
• "+" 連接字面量和非final變量援所，不優(yōu)化
• "+" 連接字面量和方法返回值，不優(yōu)化

Tip

工作中遇到為了去除重復數(shù)據(jù)而使用TreeSet的場景

TreeSet<K> set = new TreeSet<>();

java中的Set一般都是通過Map實現(xiàn)队贱，使用TreeSet的無參構(gòu)造方法實例化一個對象時色冀，實際上是通過TreeMap實現(xiàn)的，這時泛型對象K必須是實現(xiàn)了Comparable接口的對象柱嫌。TreeMap的put方法進行大小比較時锋恬，先判斷是否傳入外部比較器（Comparator），如果沒有則使用K類的Comparable接口實現(xiàn)编丘，而無參構(gòu)造器實例化時是沒有外部比較器的与学。

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