1、选择题
2、选择题答案：1-3:BAC 4： ACD 5：A4:由大小写字母、数字、下划线（_）和美元符号（$）组成，开头不能是数字。不能使用关键字6-7:CB
3、判断题
8、编程题答案1、publicclassTest2{publicstaticvoidmain(String[]args){intwidth=6;for(inti=0;i<width;i++){System.out.println("");for(intj=0;j<width;j++){intx=j+0;System.out.print(x>i?i:x);}}}}2、packagetest;importjava.util.Set;importjava.util.TreeSet;publicclassMyTest{publicstaticSet<String>set=newTreeSet<String>();publicstaticvoidperm(char[]n,intbeg,intend){if(beg==end){addNumber(String.valueOf(n));}else{for(inti=beg;i<=end;++i){swap(n,beg,i);perm(n,beg+1,end);swap(n,beg,i);}}}publicstaticvoidswap(char[]n,intx,inty){if(x==y||n[x]==n[y]){return;}chartemp=n[x];n[x]=n[y];n[y]=temp;}publicstaticvoidaddNumber(Stringstr){if(str.charAt(2)=='4'||str.contains("35")||str.contains("53")){return;}set.add(str);}publicstaticvoidmain(Stringargs[]){char[]number=newchar[]{'1','2','2','3','4','5'};perm(number,0,number.length-1);System.out.println(set.size());intcols=10;for(Strings:set){System.out.print(s+"");if(cols--==1){System.out.println();cols=10;}}}}3、Illegalmodifierforparameteraaa;onlyfinalispermitted4、Exceptioninthread"main"java.lang.NullPointerException
