Java 字符串 （二）

/**
 * String APi demo
 * @author lanluyug
 * @date 2020-02-18
 */

import java.util.Arrays;
public class stringDemo{
    public static void main(String[] args){
        testStringFun("Hello, CoreJava !");
    }

    public static void testStringFun(String testString){

        // substring
        System.out.println("substring(0,3):  " + testString.substring(0,3));

        // join
        System.out.println("String.join: " + String.join(" / ","S", "M", "L"));

        // equals & equalsIgnoreCase & == & compareTo
        System.out.println("equals: " + testString.substring(0,3).equals("Hel"));
        System.out.println("equalsIgnoreCase: " + testString.substring(0,3).equalsIgnoreCase("hel"));
        System.out.println("==: " + (testString.substring(0,3) == "Hel"));
        // 位于形参之前，返回正数， 位于形参之后，返回负数，相等返回0
        System.out.println("compareTo: " + (testString.substring(0,3).compareTo("Hel") == 0)); 

        // charAt
        System.out.println("charAt: " + testString.charAt(0));

        // 返回码点
        int index = testString.offsetByCodePoints(0, 2);  // 返回2
        System.out.println("offsetByCodePoints: " + index);
        System.out.println("codePointAt: " + testString.codePointAt(index));

        // codePoints & new String()
        int[] codePoints = testString.codePoints().toArray(); // codePoints返回intStream，java 8
        System.out.println("codePoints(): " + Arrays.toString(codePoints));
        System.out.println(" new String(codePoints, start, length): " + new String(codePoints, 0, codePoints.length));

        // startsWith
        System.out.println("startsWith: " + testString.startsWith("Hel"));

        //endsWith
        System.out.println("endsWith: " + testString.endsWith("a !"));

        // String replace(charSequence oldString, charSequence newString)
        System.out.println("replace: " + testString.replace("CoreJava", "World"));

        // StringBuilder 单线程 效率高 ; StringBuffer 多线程 效率低
        StringBuilder sb = new StringBuilder();
        sb.append("Hel");
        sb.append("lo");
        System.out.println("StringBuilder: " + sb);

    }

}