if文でも三項演算子でもない第三のIf文を書いてみる ref: http://qiita.com/mt-village/items/7d1b5560224d2675d770

file0.java

String s = null;
if (testSomeCond()) {
    s = "is true";
} else {
    s = "is false";
}
doSomething(s);

file1.java

String s = testSomeCond() ? "is true" : "is false";
doSomething(s);

file2.java

String s = If.correct(testSomeCond()).then("is true").orElse("is false");
doSomething(s);

file3.java

String s = If.correct(testSooooooooooooooooooooooooooooooooomething())
        .then("is trueeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee")
        .orElse("is falseeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee");
doSomething(s);

file4.java

public class If {
    public static BoolSaver correct(Boolean b) {
        return () -> b;
    }
}

@FunctionalInterface
public interface BoolSaver {
    Boolean get();

    default <A> Else<A> then(A a1) {
        return (A a2) -> get() ? a1 : a2;
    }
}

@FunctionalInterface
public interface Else<A> {
    A orElse(A a2);
}

file5.java

int[] a = {1,2};
int i = 3;
int result = If.correct(i < a.length).then(a[i]).orElse(-1);

file6.java

int[] a = {1,2};
int i = 3;
// 通常の書き方
int a = If.correct(i < a.length).then(a.length).orElse(i);
// 戻り値の片方が例外を発生し得る場合の書き方
int b = If.correct(i < a.length)
    .then(() -> a[i])
    .orElse(() -> -1);

file7.java

public class If {
    public static BoolSaver correct(Boolean b) {
        return () -> b;
    }
}

@FunctionalInterface
public interface BoolSaver {
    Boolean get();

    default <A> Else<A> then(A a1) {
        return (A a2) -> get() ?  a1 : a2;
    }

    default <A> ElseSaver<A> then(Supplier<A> a1) {
        return (Supplier<A> a2) -> get() ? a1.get() : a2.get();
    }
}

@FunctionalInterface
public interface Else<A> {
    A orElse(A a2);
}

@FunctionalInterface
public interface ElseSaver<A> {
    A orElse(Supplier<A> a2);
}