(DDDD)nullJavaQQQQQDDDDD1.叮 StringODDDDDDDDDDDDDDDDA.extractstring()B.substring()C.Substring()D.Middlestring()2DDDDDDDDDDDDA)HashTableDDDDDDDDDDnullB)HashTableDDDDDDDDDDDnullC)HashTableDDDDDDDnullDDDDDDD)HashTableDDDDDDDDnullDDDDD3DDDDDDDDStringstr1="java";Stringstr2="java";Stringstr3=newString("java");StringBufferstr4=newStringBuffer("java");DDDDDDDDtrueUMDA)str1==str2;B)str1==str4;C)str2==str3;D)str3==str4;4DDDDDDDDDDDDDD}8DDDDDDDDDDDDDDDDDDDD:()A)helloanddB)helloandaC)worldanddD)worldanda6DDDDDDDDDDDDODD()publicclassStringTest{publicstaticvoidmb_operate(Stringx,Stringy){x.concat(y);y=x;}publicstaticvoidmain(Stringargs[]){Stringa="A";Stringb="B";mb_operate(a,b);System.out.println(a+"."+b);}}ADA.ABDB.ACDA.BDDB.B}DDWorldWorldpublicclassTestGetChars{publicstaticvoidmain(String[]args){StringmyString=newString("HelloWorld!");char[]yourString=newchar[16];myString.getChars(6,11,yourString,0);System.out.println(myString);System.out.println(yourString);}}ADHelloWorld!BDHelloWorld!HelloHello!CDHelloWorld!World9DDDDDDDDDDDDDDDpublicclassTestStringContructor{publicstaticvoidmain(String[]args){byte[]b={49,50,51,52,53};StringmyString=newString(b);System.out.println(myString);}}AD45555BD12345CD90123DD495051525310DDDDDDDDDDDDDDDpublicclassJ_Intern}DDDDDDDDtrue(D)?(A)B)C)DDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDD15DDDA)C)myVectDDDDDDDVectorDDDDDDDDDDDVectorDDDDVectorDDDDVectorDDDDDDDDDDDDDDArrayListUMMCICIArrayListmyList=newObjectMUArrayListmyList=newListM;()B)ListmyList=newArrayListUMD)ListmyList=newListUMListUMDDDDDDDDDD}ADs2==s1BDs2==s1s3==s1s3==s1s4!=s1s4==s1s5!=s1s5!=s1s6==s1s6==s1CDs2==s1DDs2!=s1s3==s1s3==s1s4!=s1s4!=s1s5!=s1s5!=s1s6!=s1s6==s111DDDDDDDDDDDD()StringBufferbuf1=newStringBuffer(20);System.out.println(bufl.length()+U,D+bufl,capacity());A)0,20B)0,nullC)20,20D)0,014DDDDDDDDDD1)publicvoidcreate(){2}VectormyVect;3}myVect=newVector();4}}}C)s[0]DODDD)s.lengthD1017DDDDDDDDDDDDD?()A)Strings="DD";inti=3;s+=i;B)Strings="DD";inti=3;if(i==s){s+=i};C)Strings="DD";i...
