將一個字符串序列用分隔符連接起來。
1.構(gòu)造函數(shù)
只對外提供靜態(tài)Joiner.on方法來構(gòu)造joiner
public?static?Joiner on(String separator) {
????return?new?Joiner(separator);
//調(diào)用構(gòu)造方法，傳入分隔符分為字符串和字符兩種形式
}
public?static?Joiner on(char?separator) {
//字符轉(zhuǎn)換為字符串
????return?new?Joiner(String.valueOf(separator));
}
private?Joiner(String separator) {
????this.separator = (String)Preconditions.checkNotNull(separator);
}
2.檢查null
忽略空值
public Joiner skipNulls()
@CheckReturnValue
public?Joiner useForNull(final?String nullText) {
????Preconditions.checkNotNull(nullText);
????return?new?Joiner(this) {
????????CharSequence toString(@Nullable?Object part) {
????????????return?(CharSequence)(part ==?null?? nullText : Joiner.this.toString(part));
????????}
????????public?Joiner useForNull(String nullTextx) {
????????????throw?new?UnsupportedOperationException("already specified useForNull");
????????}
????????public?Joiner skipNulls() {
????????????throw?new?UnsupportedOperationException("already specified useForNull");
????????}
????};
}
public?Joiner skipNulls() {
????return?new?Joiner(this) {
?????//返回新建Joiner 檢查列表里是否有null 有null跳過
????????public? A appendTo(A appendable, Iterator parts)?throws?IOException {
????????????Preconditions.checkNotNull(appendable,?"appendable");
????????????Preconditions.checkNotNull(parts,?"parts");
????????????Object part;
????????????while(parts.hasNext()) {
????????????????part = parts.next();
????????????????if?(part !=?null) {
????????????????????appendable.append(Joiner.this.toString(part));
????????????????????break;
????????????????}
????????????}
????????????while(parts.hasNext()) {
????????????????part = parts.next();
//不等于null 添加僅
????????????????if?(part !=?null) {
????????????????????appendable.append(Joiner.this.separator);
????????????????????appendable.append(Joiner.this.toString(part));
????????????????}
????????????}
????????????return?appendable;
????????}
????????public?Joiner useForNull(String nullText) {
????????????throw?new?UnsupportedOperationException("already specified skipNulls");
????????}
????????public?Joiner.MapJoiner withKeyValueSeparator(String kvs) {
????????????throw?new?UnsupportedOperationException("can't use .skipNulls() with maps");
????????}
????};
}
Joiner joiner = Joiner.on("; ").skipNulls();
return?joiner.join("Harry",?null,?"Ron",?"Hermione");
3.join
public?final?String join(@Nullable?Object first,?@Nullable?Object second, Object... rest) {
????return?this.join(iterable(first, second, rest));
//將元素變成迭代器放入
}
public?final?String join(Iterable<?> parts) {
????return?this.join(parts.iterator());
}
public?final?String join(Iterator<?> parts) {
????return?this.appendTo(new?StringBuilder(), parts).toString();
//調(diào)用 appendTo串聯(lián)起來廉嚼，拼接字符串
}
public?final?String join(Object[] parts) {
????return?this.join((Iterable)Arrays.asList(parts));
}
public?final?StringBuilder appendTo(StringBuilder builder, Iterator<?> parts) {
????try?{
????????this.appendTo((Appendable)builder, (Iterator)parts);
????????return?builder;
????}?catch?(IOException var4) {
????????throw?new?AssertionError(var4);
????}
}
public?final?StringBuilder appendTo(StringBuilder builder, Object[] parts) {
????return?this.appendTo((StringBuilder)builder, (Iterable)Arrays.asList(parts));
}
public?final?StringBuilder appendTo(StringBuilder builder,?@Nullable?Object first,?@Nullable?Object second, Object... rest) {
????return?this.appendTo(builder, iterable(first, second, rest));
}
