Guava-1.22类Strings

public static String nullToEmpty(@NullableDecl String string)

@NullableDecl
public static String emptyToNull(@NullableDecl String string)

public static boolean isNullOrEmpty(@NullableDecl String string)

public static String padStart(String string, int minLength, char padChar)
public static String padEnd(String string, int minLength, char padChar)

public static String repeat(String string, int count)

public static String commonPrefix(CharSequence a, CharSequence b)
public static String commonSuffix(CharSequence a, CharSequence b) 

public class StringTest {
    public static void main(String[] args) {
        String s = "hello world";
        String e = "";
        String n = null;
        System.out.println(Strings.nullToEmpty(s)); // "hello world"
        System.out.println(Strings.nullToEmpty(e)); // ""
        System.out.println(Strings.nullToEmpty(n)); // ""
        System.out.println(Strings.emptyToNull(s)); // "hello world"
        System.out.println(Strings.emptyToNull(e)); // null
        System.out.println(Strings.emptyToNull(n)); // null
        System.out.println(Strings.isNullOrEmpty(s)); // false
        System.out.println(Strings.isNullOrEmpty(e)); // true
        System.out.println(Strings.isNullOrEmpty(n)); // true
        System.out.println(Strings.padStart("xx", 4, 'o')); // "ooxx"
        System.out.println(Strings.padEnd("xx", 4, 'o')); // "xxoo"
        System.out.println(Strings.repeat("xx", 3)); // "xxxxxx"
        System.out.println(Strings.commonPrefix("oooo", "ooxx")); // "oo"
        System.out.println(Strings.commonSuffix("xxxx", "ooxx")); // "xx"
    }
}