[Guava Study Notes] basic utilities: NULL, precondition, object method, sorting, exception

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Null

Guava uses optional to indicate T-type references that may be null.

Create:Optional. Of (t) does not accept nullOptional. fromnullable (t) accepts nullOptional. Absent ()

Query:Ispresent ()Get ()Or (t) if it is null, It is tOrnull ()

Others:Objects. firstnonnull (t, t) is used to specify the default value for null. If both are null, nullpointerexception is thrown.

　　　　Emptytonull (string ),Nulltoempty (string)

Prerequisites

Usage:

checkArgument(i >= 0, "Argument was %s but expected nonnegative", i);checkArgument(i < j, "Expected i < j, but %s > %s", i, j);

Checkargument (Boolean)Checknotnull (t)Checkstate (Boolean)

Checkelementindex (INT index, int size)Checkpositionindexes (INT start, int end, int size)

Inline use:This. Field = checknotnull (field)

Object Method

Objects. Equals (a, B) equals that can be nullObjects. Hash (object ...)

Tostring ():

// Returns "ClassName{x=1}"Objects.toStringHelper(this).add("x", 1).toString();// Returns "MyObject{x=1}"Objects.toStringHelper("MyObject").add("x", 1).toString();

Compare ():

public int compareTo(Foo that) {    return ComparisonChain.start()            .compare(this.aString, that.aString)            .compare(this.anInt, that.anInt)            .compare(this.anEnum, that.anEnum, Ordering.natural().nullsLast())            .result();}

Sort

Ordering: comparator implementation

Structure: natural order of natural ()Usingtostring () Lexicographic OrderFrom (comparator)

Chain call:Reverse reverse ()Nullsfirst ()Nullslast ()Lexicographical ()Onresultof (function)

Ordering<Foo> ordering = Ordering.natural().nullsFirst().onResultOf(new Function<Foo, String>() {  public String apply(Foo foo) {    return foo.sortedBy;  }});

Set and element:Greatestof (iterable, int K)Min (iterable)Min (E, E ...)

Isordered (iterable)Sortedcopy (iterable)